Question

A body of mass m is moving in a circle of radius $r$ with a constant speed $v.$ The force on the body is $\frac{m{v}^2}{r}$ and is directed towards the centre. What is the work done by this force in moving the body over half the circumference of the circle?

• A. $\frac{m{v}^2}{\pi r^2}$
• B. Zero
• C. $\frac{m{v}^2}{r^2}$
• D. $\frac{\pi r^2}{m{v}^2}$

Answer 1

Answer: (B)

Work done by centripetal force is always zero, because force and instantaneous displacement are always perpendicular

$W=\vec{F}.\vec{s}=Fs\cos \theta$

$=Fs\cos \left(90^{\circ }\right)=0$