Question

if a comet suddenly hits the moon and imparts energy which is more than the total energy of the moon, what will happen?

Answer 1

An asteroid that large striking the Moon would release a large amount of energy and it probably would eject some of the moon rock into space, however I would guess that the bits would be quite small, so if they happened to be going in the right direction to hit the Earth they wouldn't cause too much damage.

Hope this helps