For those who are thinking that these questions are quite easy and not that challenging, the main motive here is to check the approach and understanding of the student...The qualitative interceptions made by him are on point .... As an indian you might feel the calculations were too easy because of the rigorous practice we do here and the amount of training we receive while preparing for competitive exams....the aim here is not to check how well trained you are, rather it's how well you think...and how deep you think
@@dominicj7977 In fact most Indians are just well trained... it's a compulsive practice to be fast in both maths and physics , else you fail your exams here... that's what drives the ability... Yet many of us don't continue with that and fall behind the western students...
@@dev_invc Yea tell me about I had GATE AIR 110 , still couldn't make it to IITs/IISc with my score. But when I tried to apply for MS in US colleges, they ask for research and recommendations. And most importantly exorbitant fee.
@@dominicj7977 I hope you do better in future, getting into a foreign University is more qualitative though.. I am myself a STEM educator for an U.S based company, so I have a slight idea about the level of questions compared to indian standards..
Just in case people get confused, there is a small mistake at 29:40 should be (x^2 + L^2)^{-1/2) not (x^2 + d^2)^{-1/2} in the numerator of the first term for the derivative.
As someone who took his last physics class 20+ years ago, but did a fair amount of interviews for recruiting, I really appreciate the design and progression of the first two questions. It starts off with a simple second derivative, which should remind people of acceleration which is proportional to force. The equation therefore states that force is inversely proportional to displacement, the classic oscillator description. It then goes on to a floating buoy, which common sense tells us will bounce till it quiets down, so a damped oscillator. Analyzing it with a force diagram, the change in buoyancy force is proportional to change in volume submerged. But since the object is spherical, the change won’t be uniform and it causes the dampening effect. I would be looking for the interviewee to ground his explanation more in physics and link up the two parts.
Thanks for uploading. Simple harmonic motion, buoyancy and Archimedes and then Ibn Sahl's, or as said in the mock interview Snell's law of refraction, in a Baywatch kind of scenario and all mathematically treated. Thanks again.
The last time I touched a higher level physics/maths book was about a decade, however during a work day I have recommended and then decided to view an interview for Physics, FU TH-cam, also great job with the interview, you really do understand the concepts well
They’re just trying to see if the student can systematically work out a solution to these problems with logic, connect to broader points, genuinely explain every step of the way without it being spelled out for them. This is easy even if you’ve taken 1 or 2 physics classes in high school or university that spell it all out for you, but most high schools don’t cover material to this extent. It’s definitely a challenge to reorganize all your thoughts, and systematically work out steps that will get you to your solution even as a university student. The explaining is what deters you the most, and puts pressure on you.
Ya because you are from India where these questions are basic... Our intermediate (10+2) is too advanced compared to these questions yet our higher education is not that advanced moving forward...
@@dev_invc what? Higher education is not that advance... Woo I didn't know that... Maybe research and college are not un ranking but we really do study advance level stuff which are similar to what is taught in US or UK...
Everyone here boasting how laughably easy this is, what have I missed? I passed all physics courses for EE in college and the second part of that interview would basically be one of the hardest questions in the exam...
i dont mean it in a mocking way, but some countries a have relatively difficult and exhaustive curriculums which make this seem of lower difficulty... but yes these are good ques analytically
Good job! I've been in a maths intense path myself and I still find the candidate quite good. It's not as easy as it seems to navigate between physical interpretations and maths expressions. He never said anything senseless, every single word he said was relevant. He didn't rush, took the time to think and answer from basic principles and observations. The concepts look clear in his mind, he hasn't been lost in overly abstract and calculation driven tendencies. He's probably not your strongest maths intensive candidate but he looks like a good allrounder that has high chances of doing well as a Physics major which is what the interview is all about, they're not looking for Olympiad contestants.
Lol I had exactly the same question. It would be a little challening from a student straight out of highschool, althought doable if you are not in an exam enviroment but for somebody with a physics degree it should be quite simple.
Same! I thought I would not know how to answer any of the questions, or maybe not even understand them, but I actually had an idea on how to solve all of them.
These weren't difficult questions, all of it is something you could learn in AP physics, not sure what this interview is for. The undergraduate physics I did covered EM waves, Fourier, etc...
Can also imagine the land-sea question as 2 springs of different stiffness joined together. The position of equilibrium would be the exact same path of light or the minimised time path. I would mention that if you get this question :)
Eh, that's a rather abstract application which technically doesn't obey physical principles (as 3b1b pointed out himself). It's similar to the analogy that a person's displacement as they fall through the Earth is the same as one modeled by a spring (it is!). Of course you can mention it to show your passion, but using it to actually solve a problem or to show your complex understanding is a little odd as it's not a conventional solution + it can in circumstances be a 'cheat,' like with the 'falling through the Earth' question it's an oversimplification and maybe the interviewer wants to see your calculus abilities and your knowledge on approximating the force within a sphere of uniform density. In this case however, using Snell's Law would be a very intuitive approach as it is not an analogy, it is a perfectly valid solution as it solves for least time
@@dakerbal of course the go to method here is Snells law as that’s more inline with courses taught in A-level. The spring analogy is just something you can mention to show background reading or passion for physics in general.
very interesting video, i have just a question about the period of the small oscillations of the ball. When deriving the net force acting on the sphere shouldn't we consider also the force of gravity acting on the small cilinder? in that case the net force would be half of that calculated by the student. This would make also more sense since is exactly gravity that then let the ball oscillate back down.
No, the buoyant force acting on the lower half of the sphere counteracts the weight of the entire sphere, as said a little earlier. This is why he analizes the _change_ in net force on the sphere given by the change in displaced volume of water
No as the equilibrium where forces are zero is our basis reference for force, when he calculated the new Fb, this wasn't the total buoyant force, it was the addition force, which could "act" as the total force. because all other forces equate to zero
I think he is linearizing the behaviour in the equilibrium point, keeping only the first order. In this way he assumes that the difference between force pointing towards the bottom (mg) and the force pointing towards the top (Archimedes) is proportional to y, so when the sphere is above he simplifies the excess of mg contribution as an equivalent opposite force proportional to -y.
At equlibrium the buoyant force was balanced by the weight of the sphere (mg). When we push it a little downward the buoyant force increases and that excess force becomes responsible for the sphere's SHM.
Effect of atmospheric pressure on the sphere....yes but nobody mentioned...VISCOSITY of the liquid also a factor here as to how much dampened SHM gets going.(The student probably kept quiet about this as he didn't want to have to generate an equation for that too ! He he.) The last one with the life guard is very nicely thought out. The clue was using u and V as the speeds ;-) = optics... In real life there are 4 speeds to consider (gradient dependant ?) and the wind and tide vectors ! Running speed on soft sand Running speed on wet sand Running speed in the water Swimming speed in the water Effect of the tidal race windspeed and direction, on the rescuer and the casualty. The ideal lifeguard might then be able to suggest a better meeting point in the water, for example then without the casualty having to try and swim against the tide.. Local knowledge of the slope of the sea bed then comes into play , and where it’s actually shallow etc . Which gives a strange but correct final optimal path . The lifeguard would appear drunk ! Of great significance it would seem to me , would be the speed of running in different water depths . A rescuer could experiment whilst training to find out at what depth fast wading for them is slower than actually swimming. I suspect for most of us it is when the water level reaches our testimonials. In other words ONLY start swimming at that time... Its curious to note too that at all times the rescuer on any medium goes in a straight line and only makes course changes at the interfaces, Only physicists see a beach like this ! It would be so useful if lifeguards did a full on physics course at Oxford. The emotional intelligence of the student is great . Beyond his years to stay serious and professional throughout the viva. The student would fit in well at Oxford as neither have the ability to discuss the National football league table and how Arsenal have played this season. . The examiner should have said . Oh and by the way , when 2 supermassive black holes collide sometimes the spin of the resulting single mass is so excessive that all the matter is flung out by centrifugal force and expands again. . This makes quite a big bang . Does that remind you of anything? OR Perhaps there is an energy density in a quantum of space that cannot be exceeded ? The excess energy then creating more space time in a fifth dimension to accommodate this excess ? Could you write an equation for this too please ?
The math part was easy and I recognized the cos graph as used in LC oscialltion to depict charge over time , was a bit rusty in fluid mechanics oof 😳, quite interesting I enjoyed myself during the last part 😀 but it did not strike me as snells law lol .
That 2nd question was Starter pack for JEE......well that graphical concept I used during my placement they were so pleased about my unique approach and I got landed on the job..... thank you for the concept
still in A-Level at the moment...for the first differential for dt/dx: If we take f=x^1/2 so f'=1/2 x^-1/2 g=x^2 + L^2 so g'=2x+2L why would it not be 1/2 (x^2 + L^2)^-1/2 multiplied by g' ? [from what his derivative states, to me, it seems like he's only multiplied by 2x rather than (2x + 2L)... I'm sure he's correct, so any help would be appreciated!
Regarding the bit about the negligible buoyancy of the air (at around 22:00). I don t think there is any, since there is no air underneath the section of the ball to move it upwards. There is only pressure from above so i don t think it s really relevant. But if anybody has a good explanation about this please tell me. Thanks!
Interesting question. I think the buoyancy effect due to the fluid above eg air would be calculated in the normal way, even though there appears to be no bottom surface on which it can provide the buoyancy - the pressures “work through”. If it was oil above you would take into account the buoyancy effect - the weight of oil displaced. Regardless of their being no oil underneath. This may not help/ be relevant, but I think of archimedes principle by imagining a volume, which can be any shape, within a fluid ( eg a brick shape, or sphere, or anything). If the fluid isn’t moving then the upthrust on that “shape” must equal the weight of the fluid, otherwise that bit of fluid would move up, or down. Seems obvious, but I can see how it was a eureka moment. That’s why for floating ice, the weight of water displaced =upthrust = weight of the ice. So when the ice melts it must exactly fill the original volume it displaced.ie water level doesn’t change when it melts.
17:20 isn't this just the change in the buoyant force? but he later equates this to mass x acceleration, which should be equal to the total buoyant force minus the weight? I don't understand this or why he puts a minus sign on it
I don't think the approximation of the cross section of the sphere as a cylinder works at all. Wouldn't it be more like a rectangular prism especially for smaller and smaller values of dy which is what calc is all about,
Wait, how did u get a rectangular prism? If we take really small values of y, lets say dy, the 2 bases are circular and the lateral surface (with height dy) is almost perpendicular to the two circular bases. Also, if dy is infinitesimally small, the two circular bases have the same surface area. This gives us a resulting figure of a right angle cylinder with the height dy.
I mean you guys should know the volume of a solid that "winds" around the y axis. So no need for assumptions in that case. Maybe it would make things a little bit more complicated but more accurate
buoyant force repels other external forces, which is gravity here, downwards. So air would try to take up space below the volume of sphere pushing it upwards.
would it be ok if you run through the land till you create a right angle to the horizontal line to the point in the sea, by doing that it reduce the time it takes to get closer bcz as stated velocity in land is greater then the velocity in the water. by doing that it creates a line on the normal whichis the optimal solution which takes less time.
I have a question about the time 15:59, where they consider that the change of volume with the displacement y is linear! Because if we use integrals, we gone get that the change of volume is not linear, but quadratic! I'm wrong? Pls, help me on that.
You're right. It won't be linear. The radius changes considerably slowly with distance from the centre for sections of a sphere near the centre, so we can assume the radius to be constant for a small displacement.
It's mostly testing your ability to think under stress and on the spot, but also Indian education on maths and physics is much more advanced at the college level than the western world so this will be more familiar to you
Haha my guy, being interviewed is much different than being a spectator. The concepts aren't difficult at all, they're made to show thinking not to get people to fail.
This is pretty basic tbh,they're hard problems that are based on really simple concepts for the most part,i was extremely surprised when watching this bc i expected oxford interviews to be much harder
Get used to explaining your working out loud. Most applicants find the problem easy(ish) to solve, but struggle to say how they solved it in clear terms.
Oxfart, why does anyone wanna even go to this school when u can literally go to mit Stanford or some other easier school and get into FAANG and make big bucks
If I have already achieved the requisite American qualifications, but I have more AP exams in May, should I expect any potential offers (whether from oxford or elsewhere) to be conditional on basically 'exceeding' what is stated on the website? Some, but not all, of my pending scores are in subjects considered 'helpful but not required'-would a potential offer require me to score well in these exams on top of what I already have? I suppose you could only speak for Oxford, but I'm a bit confused about American qualifications and any insight/clarification would be greatly appreciated!
@@brianblumberg7599: Oooh. To study in the undergraduate level of Oxford. Thanks. Hehehe. This isn't commonplace in my country, hence the question. Thank you!
@@JesusCollegeOxford1571 will I learn everything I need to know in highschool? Or will I have to gain knowledge outside of what we’re taught? Thankyou very much for replying, also
@@gmvz712 Depends on where you go for high school. Where I went to high school we did not have anything beyond some basic physics courses. I remember distinctly our AP physics courses would never run because not enough people would sign up.
@@JesusCollegeOxford1571 You basically did a "quick recap" of our Experimental Physics I, first semester course, at uni... looks like you really need to prepare quite a lot beforehand.
Effectively, yes. The tutors can only ask questions that applicants can reasonably answer. As applicants are high schoolers, the questions will be fit for that age group. But, the questions will be a little bit surprising and force candidates to think laterally with the skills they have.
I'm slightly surprised by how reasonable these questions are for an oxford interview. I'm an Australian educator in STEM and we typically suggest that our students should do the highest levels of secondary courses to apply for ivy league schools in these fields. It is nice to see that a very competent and interested advanced math (middle tier difficulty, algebra/calculus based, year 11-12 math courses) student could probably just get through.
The questions aren’t supposed to be about the difficulty, they’re to see how the student thinks and if the person interviewing would want to teach them. It might seem strange to you but they don’t actually care about what the student knows, or think they know. The interviewers are usually going to be one of the people that will actually be teaching them. The interview is quite similar to a tutorial at Oxford or a supervision at Cambridge.
@@bgill7475 I am an upper secondary/university educator in engineering/math/physics, and I can tell you that university educators definitely care about what students know. So much so that most Australian universities will not allow entry to engineering/math/physics programs without high marks in SSCE of prep units. In Australia you cannot even be allowed to enroll in an engineering/math/physics program without having taken advanced math (Band5 (second highest band) and up) or extension math (band E3 (second highest band) and up) in year 11-12, I know this because I advise the students applying for some of these programs.
@@zakaryjaynicholls9867 Exactly, the key point being you AREN’T involved in admissions at Oxford or Cambridge, not even a university in the UK. The previous commenter is right. At these top universities, it isn’t impressive if you’ve managed to memorise a load of high school material. It’s impressive if you are able to systematically work through problems you’ve never come across, adapt your thinking to an unseen situation and have the resilience to persevere to a solution.
@@axx9149 to make it clear I do teach and advise student for entry to Ivy League institutions within Australia (the UK is not the only island with academics), I have taught a number of students at G08 institutions and over a dozen of my former students have gone to G08s. My original remark was that it was surprising that they don’t care about outright mathematical ability as we do (and many other do), just simple problem solving. I’m not saying that it’s wrong, I’m saying that as someone who thought these institutions were impressive (and full of the brightest and most hardworking people), with these entry standards I no longer consider this to be the case.
@@zakaryjaynicholls9867 I wasn’t trying to infer that top level academia is exclusive to the UK, more that the admissions process here is very different to other countries and watching one video on one part of the admissions process is not an accurate representation of the overall process. The main points that are considered in an application to Oxbridge are: predicted grades, teacher references, personal statement, PAT (physics aptitude test, in this case) score and interview performance. Since we only get 5 university choices to apply to, only the people that even apply are the ones that have a good shot at a place. They all study their subjects at the highest level possible (in this case, it’s likely to be A Level physics, maths and further maths, and possibly another subject) and are predicted to achieve top grades in all of them. Then out of those, the students that have best proven their capabilities in physics and maths in the pre-interview assessments will be selected to interview. They aren’t testing their mathematical ability here because they are already assured of it from the previous stages of admissions. Then the interview tests another important quality needed to succeed, essentially, how teachable they are. Anyway, I apologise for coming off combative in my previous comment, I should have explained what I meant better
To solve it properly yes it is fmaths, but to just sketch it as he did is not further maths all you neeD to know is first and second orDer differentiations
@@user-yr9nb2bw1m if you listen to the explanation in the video he’s explaining why the shape of the graph is sinusoidal. If you know how to solve the 2nd order DEs the general solution turns out to be y=A COS X + B SIN X where a and b are constants to be determined based on initial conditions. But just follow the explanation in the video and you can do it without knowing how to solve DEs
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For those who are thinking that these questions are quite easy and not that challenging, the main motive here is to check the approach and understanding of the student...The qualitative interceptions made by him are on point .... As an indian you might feel the calculations were too easy because of the rigorous practice we do here and the amount of training we receive while preparing for competitive exams....the aim here is not to check how well trained you are, rather it's how well you think...and how deep you think
Couldn't have said it better!
I think being Indian is over-rated in STEM subjects. A lot of people assume that jyst because you are indian, you must be some math wiz or something
@@dominicj7977 In fact most Indians are just well trained... it's a compulsive practice to be fast in both maths and physics , else you fail your exams here... that's what drives the ability... Yet many of us don't continue with that and fall behind the western students...
@@dev_invc Yea tell me about I had GATE AIR 110 , still couldn't make it to IITs/IISc with my score.
But when I tried to apply for MS in US colleges, they ask for research and recommendations. And most importantly exorbitant fee.
@@dominicj7977 I hope you do better in future, getting into a foreign University is more qualitative though.. I am myself a STEM educator for an U.S based company, so I have a slight idea about the level of questions compared to indian standards..
this was a fantastic derivation that transitions through multiple ideas in physics. i thoroughly enjoyed it
Unbelievably way over my head but still fascinating to watch
Just in case people get confused, there is a small mistake at 29:40 should be (x^2 + L^2)^{-1/2) not (x^2 + d^2)^{-1/2} in the numerator of the first term for the derivative.
smart guy
I was confused too, it's a relief to find this comment
i saw that as well (:
As someone who took his last physics class 20+ years ago, but did a fair amount of interviews for recruiting, I really appreciate the design and progression of the first two questions. It starts off with a simple second derivative, which should remind people of acceleration which is proportional to force. The equation therefore states that force is inversely proportional to displacement, the classic oscillator description. It then goes on to a floating buoy, which common sense tells us will bounce till it quiets down, so a damped oscillator. Analyzing it with a force diagram, the change in buoyancy force is proportional to change in volume submerged. But since the object is spherical, the change won’t be uniform and it causes the dampening effect. I would be looking for the interviewee to ground his explanation more in physics and link up the two parts.
Thanks for uploading. Simple harmonic motion, buoyancy and Archimedes and then Ibn Sahl's, or as said in the mock interview Snell's law of refraction, in a Baywatch kind of scenario and all mathematically treated. Thanks again.
It was very nice!! I recalled back by class 11 and 12 topics through this video
The last time I touched a higher level physics/maths book was about a decade, however during a work day I have recommended and then decided to view an interview for Physics, FU TH-cam, also great job with the interview, you really do understand the concepts well
That could have been in Chinese and I would have understood no less.
They’re just trying to see if the student can systematically work out a solution to these problems with logic, connect to broader points, genuinely explain every step of the way without it being spelled out for them. This is easy even if you’ve taken 1 or 2 physics classes in high school or university that spell it all out for you, but most high schools don’t cover material to this extent. It’s definitely a challenge to reorganize all your thoughts, and systematically work out steps that will get you to your solution even as a university student. The explaining is what deters you the most, and puts pressure on you.
Seems rather easy but would bottle it in the interview
These were all very good practices, it was well planned out so it was both questions on physics and mathematics (generalized for both)
wow... the IB formula booklets have spoilt me. I understand all the concepts but recalling all the expressions was a challenge.
Thankyou for uploading this! As a student of class 11th, I was quite surprised that I got most of the questions correct myself!
Ya because you are from India where these questions are basic... Our intermediate (10+2) is too advanced compared to these questions yet our higher education is not that advanced moving forward...
@@dev_invc what? Higher education is not that advance... Woo I didn't know that... Maybe research and college are not un ranking but we really do study advance level stuff which are similar to what is taught in US or UK...
@@dev_invcJesus you really have a problem with these Indians, you’ve commented multiple times about Indians
if he is willing to be an undergrad, he has extreme clarity over the subject. He just formulated fermat principle
As a 2nd year IB HL AI maths student I am surprised that I understand 70% of this video.
wow u must be so cool!
I'd say understanding it isn't the hard part, the hard part comes when you have to attach these concepts without it being spelled out to you.
@@josepherrami3434 exactly
As a senior in HS I’m surprised I understood 95% of this video
Why would you be surprised? The exact people doing this sort of interview would be 2nd year IB maths AI HL students or similar levels
Yeah, not going Oxford
I am grateful for having an opportunity to watch this video, it was really encouraging, thank you.
Everyone here boasting how laughably easy this is, what have I missed? I passed all physics courses for EE in college and the second part of that interview would basically be one of the hardest questions in the exam...
i dont mean it in a mocking way, but some countries a have relatively difficult and exhaustive curriculums which make this seem of lower difficulty... but yes these are good ques analytically
This is all very basic but very tricky at the same time very easy to make a mistake and forget if not recapped regularly.
I mean, this isn't rocket science, is it? Oh, it is? Damn.
Yes, it is. rocket science uses these concepts a lot.!
@@Muradsahar ...Well, d'uh.
Good job! I've been in a maths intense path myself and I still find the candidate quite good. It's not as easy as it seems to navigate between physical interpretations and maths expressions. He never said anything senseless, every single word he said was relevant. He didn't rush, took the time to think and answer from basic principles and observations. The concepts look clear in his mind, he hasn't been lost in overly abstract and calculation driven tendencies.
He's probably not your strongest maths intensive candidate but he looks like a good allrounder that has high chances of doing well as a Physics major which is what the interview is all about, they're not looking for Olympiad contestants.
Shutup, what do you know.
Surprised Mat isn’t doing this one as well!
for what purpous is this Interview exactly? A bit too hard for a before-first-semester student and waaaay to easy for anybody else.
Lol I had exactly the same question. It would be a little challening from a student straight out of highschool, althought doable if you are not in an exam enviroment but for somebody with a physics degree it should be quite simple.
@@leonidasg2257 between those two levels that you just described, there's a process of learning, right? Maybe that's what they're testing
he isnt a first semester , he said he was a 3rd year physicist . Please listen carefully
Guys this is for 2025 entry these guys are in the future catch up and make more videos like this without releasing it in your hands
@@oiajwoadgea6123 Yes, but isn't this for prospective undergraduate students? Don't be smart-mouthed.
Shout out to the 19th century moustache
I got an interview for History at Oxford last week - tell me why i'm watching physics interviews to procrastinate preparing for mine.
Lol
Congrats
My son had an interview for History with Merton last Thursday. Good luck to everyone who had their interview(s)
Thank you for the video. I got an interview invitation for physics at Oxford today
Me too in a week.😄
Which college?
@@tfl_supers5362 st John's
Good luck
Was it like this one?
Interesting topic's Lg
Lol first thing that came to my mind when I saw the question about the beach was it's similarity to refraction
After all the questions I was like wow. Physics is beautiful
He said sketch, i thought that meant draw a curve
I'm so surprised to realise that I can actually understand so much of this being in 12th grade.
Same! I thought I would not know how to answer any of the questions, or maybe not even understand them, but I actually had an idea on how to solve all of them.
12y of math is a lot mate
These weren't difficult questions, all of it is something you could learn in AP physics, not sure what this interview is for. The undergraduate physics I did covered EM waves, Fourier, etc...
Probably because the questions are intended for people in the equivalent of 12th grade.
same here, although i was confused with the terminology cause im german
Can also imagine the land-sea question as 2 springs of different stiffness joined together. The position of equilibrium would be the exact same path of light or the minimised time path. I would mention that if you get this question :)
Eh, that's a rather abstract application which technically doesn't obey physical principles (as 3b1b pointed out himself). It's similar to the analogy that a person's displacement as they fall through the Earth is the same as one modeled by a spring (it is!). Of course you can mention it to show your passion, but using it to actually solve a problem or to show your complex understanding is a little odd as it's not a conventional solution + it can in circumstances be a 'cheat,' like with the 'falling through the Earth' question it's an oversimplification and maybe the interviewer wants to see your calculus abilities and your knowledge on approximating the force within a sphere of uniform density. In this case however, using Snell's Law would be a very intuitive approach as it is not an analogy, it is a perfectly valid solution as it solves for least time
@@dakerbal of course the go to method here is Snells law as that’s more inline with courses taught in A-level. The spring analogy is just something you can mention to show background reading or passion for physics in general.
This is so easy I am already learning this in 7th grade.
Many times stood on a harbour thinking about the forces involved to keep that ship just where it is in the water. Guess some of us are just weird.
This was really encouraging thank you :)
You are very welcome! All best wishes to you
very interesting video, i have just a question about the period of the small oscillations of the ball. When deriving the net force acting on the sphere shouldn't we consider also the force of gravity acting on the small cilinder? in that case the net force would be half of that calculated by the student.
This would make also more sense since is exactly gravity that then let the ball oscillate back down.
No, the buoyant force acting on the lower half of the sphere counteracts the weight of the entire sphere, as said a little earlier. This is why he analizes the _change_ in net force on the sphere given by the change in displaced volume of water
No as the equilibrium where forces are zero is our basis reference for force, when he calculated the new Fb, this wasn't the total buoyant force, it was the addition force, which could "act" as the total force. because all other forces equate to zero
I think he is linearizing the behaviour in the equilibrium point, keeping only the first order.
In this way he assumes that the difference between force pointing towards the bottom (mg) and the force pointing towards the top (Archimedes) is proportional to y, so when the sphere is above he simplifies the excess of mg contribution as an equivalent opposite force proportional to -y.
At equlibrium the buoyant force was balanced by the weight of the sphere (mg). When we push it a little downward the buoyant force increases and that excess force becomes responsible for the sphere's SHM.
@@tilakshukla8962 smh?
Effect of atmospheric pressure on the sphere....yes but nobody mentioned...VISCOSITY of the liquid also a factor here as to how much dampened SHM gets going.(The student probably kept quiet about this as he didn't want to have to generate an equation for that too ! He he.)
The last one with the life guard is very nicely thought out. The clue was using u and V as the speeds ;-) = optics...
In real life there are 4 speeds to consider (gradient dependant ?) and the wind and tide vectors !
Running speed on soft sand
Running speed on wet sand
Running speed in the water
Swimming speed in the water
Effect of the tidal race windspeed and direction, on the rescuer and the casualty.
The ideal lifeguard might then be able to suggest a better meeting point in the water, for example then without the casualty having to try and swim against the tide.. Local knowledge of the slope of the sea bed then comes into play , and where it’s actually shallow etc . Which gives a strange but correct final optimal path . The lifeguard would appear drunk !
Of great significance it would seem to me , would be the speed of running in different water depths . A rescuer could experiment whilst training to find out at what depth fast wading for them is slower than actually swimming. I suspect for most of us it is when the water level reaches our testimonials. In other words ONLY start swimming at that time...
Its curious to note too that at all times the rescuer on any medium goes in a straight line and only makes course changes at the interfaces,
Only physicists see a beach like this ! It would be so useful if lifeguards did a full on physics course at Oxford. The emotional intelligence of the student is great . Beyond his years to stay serious and professional throughout the viva. The student would fit in well at Oxford as neither have the ability to discuss the National football league table and how Arsenal have played this season. .
The examiner should have said . Oh and by the way , when 2 supermassive black holes collide sometimes the spin of the resulting single mass is so excessive that all the matter is flung out by centrifugal force and expands again. . This makes quite a big bang . Does that remind you of anything?
OR
Perhaps there is an energy density in a quantum of space that cannot be exceeded ? The excess energy then creating more space time in a fifth dimension to accommodate this excess ? Could you write an equation for this too please ?
I would have thought surface tension would also feature
Really enjoyed that thanks
Glad you enjoyed it
Would this be considered as a successful interview?
Yes
I wouldn't refer to myself as a physicist until I was a grad student at the least?
Fairly simple
I would have asked about negative refractive index. That's a head-scratcher..
I do further maths and this hits easy
Not me 😂😭
The math part was easy and I recognized the cos graph as used in LC oscialltion to depict charge over time , was a bit rusty in fluid mechanics oof 😳, quite interesting I enjoyed myself during the last part 😀 but it did not strike me as snells law lol .
Why does Joe look like a lego man?
That 2nd question was Starter pack for JEE......well that graphical concept I used during my placement they were so pleased about my unique approach and I got landed on the job..... thank you for the concept
You have my previous pf. Tell me your story
@@amazingannyoing1716 pf?
@@niladribiswas1211 sorry, pfp. Profile picture
still in A-Level at the moment...for the first differential for dt/dx:
If we take
f=x^1/2 so f'=1/2 x^-1/2
g=x^2 + L^2 so g'=2x+2L
why would it not be 1/2 (x^2 + L^2)^-1/2 multiplied by g' ?
[from what his derivative states, to me, it seems like he's only multiplied by 2x rather than (2x + 2L)...
I'm sure he's correct, so any help would be appreciated!
It's because g' = 2x not 2x + 2L
You derive with respect to x so L^2 becomes 0
@@josefbayarsaikhan7933 ohhh right, that makes sense. thanks
Not the smart arse that you think you are.
So they didn't solve for angle (or distance x) that minimizes the time.
How did i get to this video lmao
I dont know either but its somehow relaxing to see someone do good at school.
I can verify that this is easy for someone who has done grade 12 from south Asia
Regarding the bit about the negligible buoyancy of the air (at around 22:00). I don t think there is any, since there is no air underneath the section of the ball to move it upwards. There is only pressure from above so i don t think it s really relevant. But if anybody has a good explanation about this please tell me. Thanks!
Interesting question. I think the buoyancy effect due to the fluid above eg air would be calculated in the normal way, even though there appears to be no bottom surface on which it can provide the buoyancy - the pressures “work through”. If it was oil above you would take into account the buoyancy effect - the weight of oil displaced. Regardless of their being no oil underneath.
This may not help/ be relevant, but I think of archimedes principle by imagining a volume, which can be any shape, within a fluid ( eg a brick shape, or sphere, or anything). If the fluid isn’t moving then the upthrust on that “shape” must equal the weight of the fluid, otherwise that bit of fluid would move up, or down. Seems obvious, but I can see how it was a eureka moment. That’s why for floating ice, the weight of water displaced =upthrust = weight of the ice. So when the ice melts it must exactly fill the original volume it displaced.ie water level doesn’t change when it melts.
17:20 isn't this just the change in the buoyant force? but he later equates this to mass x acceleration, which should be equal to the total buoyant force minus the weight? I don't understand this or why he puts a minus sign on it
This was pretty easy for a 12th grader.
Dude has a nice mustache btw
Damn, I thought it would be difficult
It's for 17 year olds
Pretty easy but Only weakness is in English
I don't think the approximation of the cross section of the sphere as a cylinder works at all. Wouldn't it be more like a rectangular prism especially for smaller and smaller values of dy which is what calc is all about,
Wait, how did u get a rectangular prism? If we take really small values of y, lets say dy, the 2 bases are circular and the lateral surface (with height dy) is almost perpendicular to the two circular bases. Also, if dy is infinitesimally small, the two circular bases have the same surface area. This gives us a resulting figure of a right angle cylinder with the height dy.
I mean you guys should know the volume of a solid that "winds" around the y axis. So no need for assumptions in that case. Maybe it would make things a little bit more complicated but more accurate
@@brianblumberg7599 Than we could not use a=-w^2 * y 18:08
It would not be a simple harmonic oscillator.
@@filipo4114 I would not use that formula lol. Just Google what I wrote and you'll see
@@brianblumberg7599 than there would be no simple (if any) formula for omega
Nice, I'll pass
Hate to be the cs guy but refraction question’s result can be found by binary search
Is the buoyancy force from the air pointing downwards? Since it's due to the pressure.
No upwards, the force pushes the object up
buoyant force repels other external forces, which is gravity here, downwards. So air would try to take up space below the volume of sphere pushing it upwards.
No it's not Air pressure , it would be fluid pressure so the force is upward
Will we be required to know second order differential equations?
No - the first question can be answered without knowing how to solve second order DEs (as is shown in the vid)
@@iHugoMMM bro I don’t think you know what a second order differential equation is
@@iHugoMMM you're thinking of second order derivatives not differential equations
@@reecemolloy7106 oh you're right, my bad
how can the exponentiel function get equal to zero !!
would it be ok if you run through the land till you create a right angle to the horizontal line to the point in the sea, by doing that it reduce the time it takes to get closer bcz as stated velocity in land is greater then the velocity in the water. by doing that it creates a line on the normal whichis the optimal solution which takes less time.
I have a question about the time 15:59, where they consider that the change of volume with the displacement y is linear! Because if we use integrals, we gone get that the change of volume is not linear, but quadratic! I'm wrong? Pls, help me on that.
You're right. It won't be linear. The radius changes considerably slowly with distance from the centre for sections of a sphere near the centre, so we can assume the radius to be constant for a small displacement.
Is this the same standard/difficulty of the actual interviews?
Yes it is
Why was I able to solve each question being in class 10? Just why?
It's mostly testing your ability to think under stress and on the spot, but also Indian education on maths and physics is much more advanced at the college level than the western world so this will be more familiar to you
I have zero intentions of going to Oxbridge, I don’t take Physics, why am I watching this
Same haha
missed quite a lot of shortcuts
What is this interview is for? Undergraduate degree? Or for Post graduation?
Undergraduate
I am 20 and I understood each single word. English is not even my first language. May I go to Oxford, please?
Haha my guy, being interviewed is much different than being a spectator. The concepts aren't difficult at all, they're made to show thinking not to get people to fail.
Just right Issac Newton as answer for every thing and u'll get in
You need to go to Uni if you already know this? :P
This is pretty basic tbh,they're hard problems that are based on really simple concepts for the most part,i was extremely surprised when watching this bc i expected oxford interviews to be much harder
how old is he?
why is the y have to be positive just bcause the second derivative is negative y?
because the question is d²y/dx²+y＝0，you forgot this，one is positive the other one must be negative
what should prospective applicants be taking away from this video for their own interview preparation?
Get used to explaining your working out loud. Most applicants find the problem easy(ish) to solve, but struggle to say how they solved it in clear terms.
😊😊😊😊😊😊😊😊😊😊😊😊😊😊😊
Oxfart, why does anyone wanna even go to this school when u can literally go to mit Stanford or some other easier school and get into FAANG and make big bucks
Didnt expect the questions to be that easy tbh
this does not seem that difficult. i was expecting it too be
If I have already achieved the requisite American qualifications, but I have more AP exams in May, should I expect any potential offers (whether from oxford or elsewhere) to be conditional on basically 'exceeding' what is stated on the website? Some, but not all, of my pending scores are in subjects considered 'helpful but not required'-would a potential offer require me to score well in these exams on top of what I already have?
I suppose you could only speak for Oxford, but I'm a bit confused about American qualifications and any insight/clarification would be greatly appreciated!
For Oxford you would never be asked to exceed what is stated on the website. Best wishes!
Is this an interview to get accepted at Oxford? So for 18 y/o coming from high school?
Yes, that's right. Usually 17 y/o
Kinda simple only
Shouldnt the equilibrium of the sphere in the fluid he drew be higher? At around 15:00
As an indian student this is simple 10 th grade physics...damn...fun
fam im in uni and i dont get wats going on
lmaoooo funniest thing that I read today
This is very easy i could have completed it in primary school before final year SATS very easy
Bruh you skipped mid-high school homie.
Ya shall go to skool.
Forgot you must be the new Einstein or Stephen Hawkings.
May I ask what is this Physics interview for? Is the interviewee trying to land a job in Oxford?
To study as an undergrad lol. I'll be nice to you so I won't say anything else
@@brianblumberg7599: Oooh. To study in the undergraduate level of Oxford. Thanks. Hehehe. This isn't commonplace in my country, hence the question. Thank you!
Is this like an interview for getting into Oxford
Yes, it is.
@@JesusCollegeOxford1571 will I learn everything I need to know in highschool? Or will I have to gain knowledge outside of what we’re taught? Thankyou very much for replying, also
@@gmvz712 High school.
@@gmvz712 Depends on where you go for high school. Where I went to high school we did not have anything beyond some basic physics courses. I remember distinctly our AP physics courses would never run because not enough people would sign up.
@@JesusCollegeOxford1571 You basically did a "quick recap" of our Experimental Physics I, first semester course, at uni... looks like you really need to prepare quite a lot beforehand.
What is this interview for. I could have answered all the questions, in 12 grade. Interviews aren't supposed to be that easy, are they?
This interview is probably for admission to undergraduate studies
@@amalantony8594 again it is still easy from an average Indian high schooler pov
is it post grad or undergrad
Undergrad
was this a successful interview?
Yes, it would be.
is this real oxford or some other college
Real Oxford
Is this high school level?
Effectively, yes. The tutors can only ask questions that applicants can reasonably answer. As applicants are high schoolers, the questions will be fit for that age group. But, the questions will be a little bit surprising and force candidates to think laterally with the skills they have.
I'm slightly surprised by how reasonable these questions are for an oxford interview. I'm an Australian educator in STEM and we typically suggest that our students should do the highest levels of secondary courses to apply for ivy league schools in these fields. It is nice to see that a very competent and interested advanced math (middle tier difficulty, algebra/calculus based, year 11-12 math courses) student could probably just get through.
The questions aren’t supposed to be about the difficulty, they’re to see how the student thinks and if the person interviewing would want to teach them. It might seem strange to you but they don’t actually care about what the student knows, or think they know. The interviewers are usually going to be one of the people that will actually be teaching them. The interview is quite similar to a tutorial at Oxford or a supervision at Cambridge.
@@bgill7475 I am an upper secondary/university educator in engineering/math/physics, and I can tell you that university educators definitely care about what students know. So much so that most Australian universities will not allow entry to engineering/math/physics programs without high marks in SSCE of prep units. In Australia you cannot even be allowed to enroll in an engineering/math/physics program without having taken advanced math (Band5 (second highest band) and up) or extension math (band E3 (second highest band) and up) in year 11-12, I know this because I advise the students applying for some of these programs.
@@zakaryjaynicholls9867 Exactly, the key point being you AREN’T involved in admissions at Oxford or Cambridge, not even a university in the UK. The previous commenter is right. At these top universities, it isn’t impressive if you’ve managed to memorise a load of high school material. It’s impressive if you are able to systematically work through problems you’ve never come across, adapt your thinking to an unseen situation and have the resilience to persevere to a solution.
@@axx9149 to make it clear I do teach and advise student for entry to Ivy League institutions within Australia (the UK is not the only island with academics), I have taught a number of students at G08 institutions and over a dozen of my former students have gone to G08s. My original remark was that it was surprising that they don’t care about outright mathematical ability as we do (and many other do), just simple problem solving. I’m not saying that it’s wrong, I’m saying that as someone who thought these institutions were impressive (and full of the brightest and most hardworking people), with these entry standards I no longer consider this to be the case.
@@zakaryjaynicholls9867 I wasn’t trying to infer that top level academia is exclusive to the UK, more that the admissions process here is very different to other countries and watching one video on one part of the admissions process is not an accurate representation of the overall process. The main points that are considered in an application to Oxbridge are: predicted grades, teacher references, personal statement, PAT (physics aptitude test, in this case) score and interview performance. Since we only get 5 university choices to apply to, only the people that even apply are the ones that have a good shot at a place. They all study their subjects at the highest level possible (in this case, it’s likely to be A Level physics, maths and further maths, and possibly another subject) and are predicted to achieve top grades in all of them. Then out of those, the students that have best proven their capabilities in physics and maths in the pre-interview assessments will be selected to interview. They aren’t testing their mathematical ability here because they are already assured of it from the previous stages of admissions. Then the interview tests another important quality needed to succeed, essentially, how teachable they are. Anyway, I apologise for coming off combative in my previous comment, I should have explained what I meant better
Is the first question further maths?
@@fmilhench3378 fr? I've not been taught this
To solve it properly yes it is fmaths, but to just sketch it as he did is not further maths all you neeD to know is first and second orDer differentiations
I think solving differential equations is in further maths.
@@captainhd9741 Nah not with implicit differentiation which is year 2 pure
@@user-yr9nb2bw1m if you listen to the explanation in the video he’s explaining why the shape of the graph is sinusoidal. If you know how to solve the 2nd order DEs the general solution turns out to be y=A COS X + B SIN X where a and b are constants to be determined based on initial conditions. But just follow the explanation in the video and you can do it without knowing how to solve DEs
as a junior college student of india this is easy af
日本の大学入試レベル
we here in india do such problems in 11th.