LAST Question from Cambridge Admission Exam

[@zhelyo_physics]

Thank you SO MUCH for 30 000 + subscribers this week! I cannot express how much I have loved doing these videos ever since I started filming physics in my garden during lockdown! Thank you for being part of this physics community!!

[@kingpran4420]

Congratulations! You deserve it!

[@zhelyo_physics]

@@kingpran4420 thanks a lot!

[@charliecooper7458]

Hi, please keep up making all these videos, you’re literally the #1 physics man on youtube, if i get into cambridge it’s only because of you

[@zhelyo_physics]

will do, thanks a lot for your kind comment!

[@miolio.]

Thank you so much for these solutions! You explain everything so well and I feel a lot more confident about the exam this week since finding your videos! :)

[@zhelyo_physics]

thank you so much for the comment! Much appreciated and good luck!

[@HhjMhh-r5c]

This is by far the worst NSAA/ENGAA question I ever tried preparing for it last year. You explained it very well

[@zhelyo_physics]

thanks a lot for the comment! It is very tricky on a number of levels including time pressure. If anyone finds an easier way please let me know! I also thought about plugging in numbers after I found the resistance but I think checking all the answers might have taken longer than doing the algebra.

[@sumukhadiraju5282]

Wow, thanks a lot for this solution, I just could not solve this one! Could you please post a video with any last minute strategy tips? That would be really helpful!

[@zhelyo_physics]

Anytime! Glad this is helpful! I actually made a similar video a couple of years ago if it's useful: kzbin.info/www/bejne/aofJeH54o9pnjbc

[@sumukhadiraju5282]

@@zhelyo_physics Thanks, that great! Could you also possibly solve some Cambridge interview questions? I would really appreciate help with those.

[@zhelyo_physics]

Here are some interview tips too : ) kzbin.info/www/bejne/rn-qeXushNqqracsi=4OD6NQjfosqrvQzl Good luck!

[@umutcan450]

Thanks a lot for nice question, I'm so pleasure if you solve more question circuit analysis theory

[@zhelyo_physics]

thanks a lot for the comment! Will do.

[@fallenfoxy25]

These are the type of questions you dont even bother trying to solve, even knowing the method in advance the algebra just takes far too long.

[@zhelyo_physics]

very often this is the case. Training up speed and with some luck you might have enough time to tackle the last few. Interestingly I thought the last question from the years after were quite a bit easier with a tricky integration technique but then easy algebra (much better).

[@muntahamahmud1999]

My dear brothers and sisters please pray for the people of Palestine and speak up against the genocide.#freepalestine🇵🇸🇵🇸🇵🇸

[@ziyanli-v2z]

Really help me a lot especially for the exam 2 days later!!!❤

[@nikiniewerth8148]

What a saviour! Everybody is here to prepare for tomorrow :)

[@zhelyo_physics]

good luck tomorrow everyone!

[@aryannaithani-x3m]

Rays of light that strike a tree pass through small openings in the dense foliage producing elliptically shaped pinhole images of the Sun on the ground. The images appear circular when the screen is held at an angle of 18 degree from the ground with a diameter of 5.00cm. The centre of the circle is 1.80m away from the trunk of the tree. What is the density of the sun.,, sir i have a doubt in this question , it was from out national olympiad camp

[@zhelyo_physics]

wait, the density of the sun? how? : )hmmm

[@sarojinideshpande1227]

Hi, could you please explain the answer to PAT 2017 Q18 part c (what frequency you would hear) ?

[@zhelyo_physics]

This is a tricky question! so v=f*lambda, i.e. frequency=v/wavelength, the previous part of the question ask you to express the speed and the wavelengths. Hope this helps! Good luck!

[@totallanguage]

Hello! I wanted to ask do you by any chance know any free physics class (from basics) or resources? I’m 14 right now and you really inspired me to learn physics. Thank you

[@zhelyo_physics]

thank you so much! This playlist is A Level Physics and is about 12,13 hours: kzbin.info/aero/PLSygKZqfTjPC3hJ7nRSnnXTw3tI_o67dR&si=AIgfXIEmhe-CCr-E Good luck! This would be an amazing start at physics! There is also this one on my other channel which you might find useful: kzbin.info/aero/PLYwNW8Dp_cOizH9dwTyKHFDDvfJojdk5c&si=KwSXzxbZ26bivDZv

[@totallanguage]

Thank you very much! I had a goal to participate in the ipho one day(hopefully) I will study hard!!

[@nikiniewerth8148]

Hi there, not sure you will have time to get to this but why can we not just express the power in terms of the resistance, R? Surely by differentiating this we find maximum power dissipation occurs when r=R and hence we get a different expression... Can you explain where I am going wrong?

[@zhelyo_physics]

No worries! So P=VI and P=I^2R are equivalent, i.e. R=E/I-kI^2 , so I^2R will given us EI-kI^4, which equivalent to what's in the video and when differentiated will give the same answer. Hope this helps!

[@nikiniewerth8148]

@@zhelyo_physics Surely P=I^2R, and E=I(R+r) will give P=(RE^2)/(R+r)^2 ...? And then doing the derivative with respect to R and we get dP/dR = (E^2(r-R))/(R+r)^3. Then it will =0 when R=r. So then R=kI^2, E=2RI, and brief rearrangement gives R=((kE^2)/4)^(1/3)? I must be going wrong somewhere but I can't pinpoint where...

[@zhelyo_physics]

@@nikiniewerth8148 ah so you are taking P=EI but E is the emf which is not equal to the voltage across the resistor, V, as there is internal resistance now. : ) Hope this helps!

[@nikiniewerth8148]

@@zhelyo_physics I don't think I was taking P=IE. If we say P=IV, V=(ER)/(r+R), and I=E/(R+r) From {E=V+Ir => E=I(R+r)}. Putting these together gave me the P=(RE^2)/(R+r)^2. And then following what I said previously. Sorry for this :D, I don't want to be annoying!

[@zhelyo_physics]

I just did your working out and I got the same answer, however it just dawned on me while I was working it out. We can't differentiate the power with respect to R and treat everything as a constant. The power depends on the current, which depends on the resistance and it also depends on the internal resistance. By differentiating with respect to R we are treating r as independent of the current, variable resistor which is not true. Excellent point and comment, made me think!

[@Zodiaczero2]

I love your standard model T shirt, truly a model fashion :)

[@zhelyo_physics]

haha thanks! Got it from CERN! : )

[@zhelyo_physics]

All my ENGAA solutions are in this playlist guys: kzbin.info/aero/PLSygKZqfTjPDx76OkugAocgZ_GCqwhO5_&si=ZtqOUi0hnRa0WV9m Good luck next week!

[@yemialaka9650]

Thanks for this video (although I preferred the method from the previous video). Sitting the exam this Wednesday (hopefully it goes well) could you to look at some questions from the 2022 paper? (section 2 Q2 and 12 and section 1B Q32) Im having trouble with

[@zhelyo_physics]

thanks a lot for the comment! I am not sure if I will be able to film before the exam but here is a solution to one of them, Q2 from section 2. The spring will have two forces acting on it: 1) the simple weight of the 30 kg mass, we use F=kx1 where x1 is the compression due to weight alone, x1=F/k=30*10/3000=0.10 cm. This would be the extension if weight alone acted and the lift wasn't accelerating. 2) Now, the lift is going down - this means that some of the normal reaction is removed as the floor is accelerating away from under you. This acceleration will try to extend the spring by: F=kx2, where x2 is the extension of the spring due to lift movement only, x2=F/k=ma/k=30*2/3000=0.02. 3) take away the 1 and 2 as they act in different directions to get =0.08 m, i.e. 8 cm I'll see if I have time to look at the other ones tomorrow. If anyone else has solved them already feel free to comment as well : ) Good luck everyone!

[@yemialaka9650]

Thank you so much for the solutions, u are the best! :)@@zhelyo_physics

[@JMU0]

Hello Mr 👋 I used to watch your videos and I liked your way of presenting a topic. I want to ask you a question, as a physicist. I hope you don't think that I am an idiot or that I do not know what scientific and logical thinking is. I studied physics and delved deeply into it and its philosophy, and everything that happened around me became related to it. But . . . It began to bother me to think about the question: Are there magical forces that cannot be explained by physics? Does religion have anything to do with this? I would like to ask you the same question, intending to know your opinion. Thank you.

[@zhelyo_physics]

Thanks for watching and your kind words! Physics and philosophy are very interesting but I can't really comment much about it I am afraid, as I am no expert. Have a great day!

[@ziyanli-v2z]

Really help me a lot especially for the exam 2 days later!!!❤ 1:42

[@zhelyo_physics]

Glad to hear! Good luck on the exam!

[@aadithc4389]

All my homies hate this question 😤😤😤

[@zhelyo_physics]

I don't blame them! It's tricky