IIT JEE Advanced 2016 Question on Rotation - Updated and Correct Solution

Following is the question asked in JEE Advanced 2016. This is the updated solution.
Q. Two thin circular discs of mass m and 4m, having radii of a and 2a, respectively , are rigidly fixed by a massless, rigid rod of length l =root(24)a through their centers. This assembly is laid on a firm and flat surface, and set rolling without slipping on the surface so that the angular speed about the axis of the rod is 'w' (omega). The angular momentum of the entire assembly about the point 'O' is L.
Which of the following statement (s) is (are) true ?
(A) The magnitude of the z-component of L is 55 ma^2(w).
(B) The magnitude of angular momentum of the assembly about its centre of mass is 17 ma^2(w/2).
(C) The magnitude of angular momentum of centre of mass of the assembly about the point O is 81ma^2(w).
(D) The centre of mass of the assembly rotates about the z-axis with an angular speed of (w/5).
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#rotation #angularmomentum #jeepyq #jeequestions #jeephysics

[@Visual-Physics]

Try 100+ topics for Free on App - Master each topic with animated theory videos and selected practice questions of JEE and NEET level.
Android/iOS App : visualphysics.page.link/install
Windows App : apps.microsoft.com/detail/9P5QB94CG8N8?hl=en-in&gl=IN
Website: bit.ly/3rGdUeE

[@schrodinger-mr8qz]

Thank you so much sir , you explained the question in a easy way , and the animation was really great
And yea welcome back sir

[@MajidAjaz1371]

Please upload more and more videos like this on Class 11th and 12th physics on a regular basis.🙏

[@ArthBachhuka]

Even my caching teacher sent this video for reference , amazing

[@sivaparakashs3968]

I think better will be like 17/2 ma²w + angular momemtum of masses wrt COM by considering relative velocities of masses wrt com which will be coming perpendicular to the rotational axis which will be easier i think.

[@user-gx4ed2ke4m]

Very good solution

[@sanjayjoshi1420]

Wow fantastic solutions

[@meenudubey9476]

I think its also not absolutely correct as there difference in angular momentum about point than axis(its just component). Here L about com contributed by along rod is correct but in vertical not so as body isnt symmetrical (both discs of different sizes)

[@AIM2024-tn4gg]

are you back ?

[@padhlekyakarrhahaituyahanp1011]

We don't read inertia tensor in 11th and 12th so i think this solution is no godd

[@Visual-Physics]

Hey @padhle...We have just introduced the concept to derive the correct formula to be used. You just need to know the formula to solve the question and that is already part of the syllabus.

[@padhlekyakarrhahaituyahanp1011]

@@Visual-Physics yeh appreciate that you are trying to teach with new concept but this concept is not in syllabus of jee so it is not a solution for us

[@Future_IITian2024]

brother exam mein method chahe course mein ho ya nahi kya fark padta….bas woh valid hona chahiye that’s the criteria….ex sir ne theorem of Papus bhi bhi padaya tha for calculating center of mass…it is also not in our syllabus but it is best method for cal. Com

[@adityasart2644]

​@@Visual-Physicsyes this is not given in any book and not taught in coachings then how we do

[@shreyash5950]

​@@adityasart2644 Bro I think if u need to be an IIT'an With under 10 AIR then u don't have to focus on syllabus and books , it's all about more broad thinking of that subject ,
And for most of people these questions are simply waste of time...just my opinion

[@EdwardSnowden125]

00:30 can this be proved? Or is that a defined quantity?

[@noelgeorgi3313]

It can be, just put the thing (equation) that defines the particular point of com in the defining equation of angular momentum as the moment of momentum

[@user-st8eu2nc6g]

T = 2pie by omega kese aya 6.30

[@SamhithVij]

Time period, he just told you that after one revolution of the disc as it's rolling without slipping it covers as distance of 2π/5 a from there he found angular velocity component along that axis

[@Future_IITian2024]

Sir plz make more tricks for rotation motion topics

[@Visual-Physics]

Hi. You can find many such questions with video solution in Visual Physics App. Download the app from here - visualphysics.gsc.im/1/ytdesc

[@RahulKar-j7t]

Wrong