Question

A ring and a disc of different masses are rotating with the same kinetic energy. If we apply a retarding torque τ on the ring, it stops after completing n revolution in all. If the same torque is applied to the disc, how many revolutions would it complete in all before stopping?

Options

• 4n

• 2n

• n

• n/2

Answer 1

n

Explanation:

Because kinetic energy K_R and retarding torque τ are the same, therefore in accordance with the relation,

Loss in kinetic energy = Work done by the torque

= τ.θ

= τ.2πn

So, both the ring and disc stop after completing an equal number of revolutions n.