Question

A ring, a solid sphere and a thin disc of different masses rotate with the same kinetic energy. Equal torques are applied to stop them. Which will make the least number of rotations before coming to rest

• A. Disc
• B. Ring
• C. Solid sphere
• D. All will make same number of rotations

Answer 1

Answer: (D)

All will make same number of rotations

Answer 2

As $W = \tau\theta$ = Energy ⇒ $\theta = \frac{\text{Energy}}{\tau} = 2n\pi$

So, if energy and torque are same then all the bodies will make same number of rotation.