Question

How much work is done on a body whirling on a circular path of radius 5 m

Answer 1

In physics, work done is said to be done only when a force is responsible for the displacement.

Mathematically it is the product of force and displacement. However, if the force and displacement are perpendicular to each other then the work done is zero. Also, if the displacement is zero the work done is zero.

Now when a body is in a circular path the force keeping the body in the circular path is the centripetal force. The centripetal force is always directed towards the center of the circle. Since, the force is along the radius and we know radius is always perpendicular to a point in the circular path. So, the force here is perpendicular to the displacement at any instant of the body. Hence, work done is zero.