standing on a icy pond you throw a 0.5 kg ball at 40 m/s you move back at 0.4 m/s after throwing what is it's mass

Asap and show ! a 14 kg rock starting from rest free falls through a distance of 5.0 m with no air resistance. find the momentum change of the rock caused by its fall and the resulting change in the magnitude of earths velocity. earth mass is 6.0 * 10^24 kg. show your work assuming the rock earth system is closed.