JEE Main 2020PhysicsRotational MotionEasyMCQ

JEE Main 2020 — Rotational Motion Question with Solution

JEE Main 2020 (07 Jan Shift 1)

Question



As shown in the figure, a bob of mass m is tied to a massless string whose other end portion is wound on a fly wheel (disc) of radius r and mass m. When released from rest the bob starts falling vertically. When it has covered a distance of h, the angular speed of the wheel will be:

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Show full solutionCorrect option: A
Correct answer
A1r4gh3

Step-by-step explanation

Using work-energy theorem 

mgh=12mv2+12Iω2

mgh=12mω2r2+12mr22ω2    ( since I=mr22 and v=rω )

mgh=34mω2r2

Hence, ω=4gh3r2=1r4gh3

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About this question

This is a previous-year question from JEE Main 2020, covering the Rotational Motion chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.