Question

Cite two examples in which a force is exerted on an object without doing any work on the object.

Short answer

Two examples where the exerted force does no work are

1. A person carrying a suitcase on his head and walks, and

2. A person is revolving a piece of stone tied to a rope around himself at constant speed.

Step-by-step solution

Step 1:Concept

There is no work done when the force exerted is perpendicular to the displacement.

Step 2:Examples where the exerted force does no work

When a person carries a suitcase on his head and moves from one point to another, no work is done. This is because the force exerted on the suitcase is upward which balances the gravitational force on the suitcase. The displacement is horizontal. Thus the force is perpendicular to the displacement and no work is done.

When a person is revolving a piece of stone tied to a rope with constant speed around himself, no work is done. This is because the force applied by the person on the rope and the stone is radially inward which balances the centripetal force, whereas the displacement is tangential. Thus the force is perpendicular to the displacement and no work is done.