Question

The moon revolves around the earth because the earth exerts a radial force on the moon. Does earth perform work on the moon?

Answer 1

No,the work done in this case is zero.

We know, work done(`W`) is defined as the scalar product of the force(`vec F`) and displacement(`vec s`)

So, `W = vec F . vec s = |vec F| |vec s| cos theta` (where, `theta` is the angle between the force and displacement vector)

Now,here the radial force exerted on the moon by the earth i.e the attractive force due to gravity acts in a direction,perpendicular to which,the moon suffers the displacement during rotation.

So, `theta =90` hence `cos theta = 0`

So, `W = |vec F| |vec s| *0=0`