Question

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

• A. no
• B. yes, sometimes
• C. yes, always
• D. cannot be decided

Answer 1

The correct option is A no

No, the earth does not perform any work on the moon.

Work done(W) is defined as the scalar product of force(F) and displacement(s).

So, W = F $\ast$ s = FsCos$\theta$ where \theta is the angle between force and displacement vector.

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

So, $\theta$ = 90 hence Cos$\theta$ = 0

So, W = |F||s| $\ast$ 0 = 0

Hence work done by earth is zero.