The magnitude of gravitational potential energy of the moon earth system is U with zero potential energy at infinite separation. The kinetic energy of the moon with respect to the earth is K.

Explanation

`U (r) = (-GMm)/(r )`
Where M is mass of the earth, m is the mass of the moon and r is their distance of separation,
` F = (-U( r))/(r ) = - GMm ( (-1)/(r^2)) = (GMm)/(r^2)`
The force F provides the centripetal force for the moon to go around
` (GMm)/(r^2) = (mv^2)/( r) rArr mv^2 = (GMm)/(r) " or " K = 1/2 mv^2 = (GMm)/(2r)`
If we take U as the magnitude of potential energy
` rArr U = (GMm)/(r ) rArr K =U/2`
hence U gt K`