When a satellite revolves around the earth in a circular path, its displacement in any short interval of time is along the tangent to the circular path of the satellite. The force of gravity acting on the satellite is along the radius of the earth at that point. Since a tangent is always at right angles to the radius, therefore, the motion of a satellite and force of gravity are at right angles (90 � angle) to each other.

Now, work done W = F Cos 90 � × s.

Since Cos 90 � = 0, therefore,

Work done W = F × 0 × s = 0

Thus, the work done by the force of gravity on a satellite round the earth is zero.