JEE Main 2019PhysicsRotational MotionHardMCQ

JEE Main 2019 — Rotational Motion Question with Solution

JEE Main 2019 (10 Apr Shift 1)

Question

Two coaxial discs, having moments of inertia I1 and I12 , are rotating with respective angular velocities ω1 and  ω12 , about their common axis. They are brought in contact with each other and thereafter they rotate with a common angular velocity. If Ef and Ei are the final and initial total energies, then Ef-Ei is:

Choose an option

Show full solutionCorrect option: D
Correct answer
D-I1ω1224

Step-by-step explanation

As external torque is zero, angular momentum remains conserved.
I1ω1+I12ω12=I1+I12ω
∴ Common angular velocity ω=5ω16
∴ Ef-Ei=12×I1+I12ω2-12×I1ω1 2-12×Il2ω122
=12×3I1256ω12-916I1ω12
=75 I1ω12-81 I1ω12144
=-6I1ω12144
=-I1ω1224

Practice this on the real CBT interface

Solve this JEE Main question (and the rest of the Rotational Motion chapter) on PrepSharp's TCS iON-style CBT player — with timer, bookmarks and session analytics.

Solve interactively →

About this question

This is a previous-year question from JEE Main 2019, 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.