JEE Main 2020 — Rotational Motion Question with Solution
From: JEE Main 2020 (Online) 2nd September Evening Slot
Question
Two uniform circular discs are rotating
independently in the same direction around
their common axis passing through their
centres. The moment of inertia and angular
velocity of the first disc are 0.1 kg-m2 and 10
rad s–1 respectively while those for the second
one are 0.2 kg-m2 and 5 rad s–1 respectively. At
some instant they get stuck together and start
rotating as a single system about their common
axis with some angular speed. The kinetic
energy of the combined system is :
Choose an option
Show full solutionCorrect option: A
Correct answer
A
Step-by-step explanation
Angular momentum conserved for the system
I1 + I2 = (I1 + I2)
0.1 × 10 + 0.2 × 5 = (0.1 + 0.2) ×
=
Kinetic energy of combined disc system
=
=
=
I1 + I2 = (I1 + I2)
0.1 × 10 + 0.2 × 5 = (0.1 + 0.2) ×
=
Kinetic energy of combined disc system
=
=
=
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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.