# I need Help. Rotational Kinetic Energy of Earth and the Moon.

## Homework Statement

What is the ratio of the rotational kinetic energy of the Earth to the rotational kinetic energy of the Moon as they spin about their axes?

## The Attempt at a Solution

Me = Mass of Earth (5.97 × 1024 kg)
Re = Radius of Earth (6.37 × 106 m)
Mm = Mass of Moon (7.35 × 1022 kg)
Rm= Radius of Moon (1.74 × 106 m)

this is all i know I don't know where to start. I know KE=(1/2)(moment of inertia)(angular velocity)

$$I = \frac{2}{5}MR^2$$