JEE Advanced Physics 2015 Paper 1 #12 (#4) Angular Momentum

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Given: A ring of mass N and radius R is rotating with angular speed omega0 about a fixed vertical axis through its center with 2 point masses m at rest at the center. The 2 masses can move along the 2 mass-less rods with out friction. At an instant omega=(8/9)omega0 and m1, is at (3/5)R from the center.
Find: Where is m2?

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[robinchoo]

The problem is the LHS of the angular momentum calculation should not be M but rather M+2m OR (10/8)M

[Bhooshan_Jape]

Good job Michel! I am a physics instructor from India and I train students for jee advanced exam( earlier called iitjee) . Aspirants of IITs ( India’’s premier engineering institutions) have to crack jee advanced.
It is perhaps the toughest undergraduate entrance test globally. Physics and maths questions of jee advanced are amazing. Thanks for taking them up in your channel. Expecting more 👍👍👍

[foxhound]

The issue I is see here, is if the one mass moved 4/5 out, and the other mass only moved 3/5 out, the center of mass of the system would have shifted off the center of rotation. If the center of mass is rotating around, it must be exchanging momentum with something external to my system. As such, there is an artificial constraint here in the way the problem is presented.

[bbartt]

Hmm, the method based on conservation of angular momentum seems fine, but something does not feel right here. It does not take into account relative position of rods, so let's assume rod 1 very very close to the rod 2, they nearly overlap. Applying the method will yield same result as presented, but since these two in the new setup are nearly the same (almost same position, etc) the result should definitely be the same for m1 and m2 and yet we'll get 3/5 for m1 and 4/5 for m2

[devalpatel]

This is unfair, you have choosen the easiest question of the advanced examination

[myanksingh]

Sir mass is different hence body has different position.

[prateekpathak]

Well these kind of questions are given to consume time of student. If student has logic then he would be correct and if student is parrot then he will be correct but will lost his precious time in the exam for other questions.

[prashantajabe]

Hii Sir, I study physics and maths well but when it come to apply those concepts to solve problem I got stuck.and then give up.
How to learn to apply concepts to solve problems?

[sujitkumardash]

I gave the JEE Advanced & now I see only grace marks work 😂