What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.

The work done by the force of gravity on a satellite moving round the earth is zero. Here's why:

1. Work done (W) is defined as the dot product of force (F) and displacement (d). In mathematical terms, W = F.d.cosθ, where θ is the angle between the force and the direction of displacement.

2. In the case of a satellite moving around the earth, the force of gravity acts towards the center of the earth. However, the satellite moves in a direction perpendicular to the force of gravity (it moves in a circular path around the earth).

3. Therefore, the angle θ between the force and the direction of displacement is 90 degrees.

4. The cosine of 90 degrees is zero. Therefore, the work done, W = F.d.cos90 = F.d.0 = 0.

So, even though the satellite is constantly being acted upon by the force of gravity, the work done by this force is zero because the force and displacement are perpendicular to each other.