First slide

Rotational motion

Question

A ring and a disc of different masses are rotating with the same kinetic energy. If we apply a retarding torque T on the ring it stops after making n revolutions, then in how many revolutions will the disc stop under the same retarding torque?

Moderate

A

n
B

2n
C

4n
D

n/2

Solution

Work done in stopping = Change in KE = Final KE - Initial KE,
i.e. $τθ$ = K = constant.
As $τ$ is same in the two cases, $θ$ must be same, i. e. number of revolution must be same.
.

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