Question

Work done by a satellite revolving around the earth is zero

Answer 1

Work done by a satellite revolving around the earth is zero because the displacement would be zero as the satellite returns back to its original position and not because the angle between force and displacement is 90 degrees.

Answer 2

it is because work done = F×S
here s =0 as displacement of the satellite
hence W .D =F × 0 = 0