Question

A boy is rotating a stone of mass $500g$ by using a string of length $50cm$ in a circular motion, with a speed $10cm/s$. What will be the work done by the force applied by the boy?

• A. $0.01\mathrm{\pi }\mathrm{J}$
• B. $\mathrm{\pi }\mathrm{J}$
• C. $10\mathrm{\pi }\mathrm{J}$
• D. zero

Answer 1

The correct option is D

zero

1. When a stone is whirled in a circle, the displacement is tangential and the centripetal force acts radially inward.
2. The angle between the radius and tangent is $90°$.
3. Work done is expressed as $W=Fs\cos \theta$, where F is the force, s is the displacement and $\theta$ is the angle between the force and the displacement.
4. When $\theta =90°$, $\cos \theta =0$ and $W=0$.
5. The work done by the centripetal force is zero.

Hence, the correct option is D.