Question

The Earth rotates around the sun due to gravitational force of the Sun. What is the work done by the force if the Earth completes half the rotation ?

Answer 1

The work done is always zero as gravitational force acts as a centripetal force.

Answer 2

The work done is zero because ... displacement is in the direction of earth (circular) and a CENTRIPETAL force is directed towards the centre. A tangent drawn at any point of the movement of the Earth shows the direction of displacement at that point. At every point, it is seen that the direction of displacement is always normal to the direction of force (or ¢ = 90). We know,

Work done = F.S cos ¢
where F is the Force and S is the displacement
=> Work done = F.S cos 90
=> Work done = F.S x 0
(since cos 90 = 0)
Hence, work done is zero....