Chapter 6, Problem 1CQ

To determine

Whether the work done on an object by external force is zero, if the object moves in a circular path.

Answer to Problem 1CQ

If the velocity is constant then the work done will be zero, otherwise there will be work done by external force.

Explanation of Solution

Write the expression for work done.

  $W=Fd\cos \theta$

Here, $F$ is the force, $d$ is the displacement, and $\theta$ is the angle between applied force and displacement.

If the velocity is a constant then work done will be zero, since the accelerating force is radial, and motion is tangential, thus the above equation will be zero.

If the angular velocity is changing then there will be a net tangential force. If the angular velocity is increasing then work is being done on mass, and if it is decreasing, then mass is doing work.

Conclusion:

Therefore, the velocity is constant then the work done will be zero, otherwise there will be work done by external force.