Arock bounces down a mountain. when will its kinetic energy be greatest?

The rock gains its maximum amount of K.E before striking the ground surface

Explanation:

When an object is comprised of certain energy due to its relative height, then it is known as the potential energy (P.E) and when an object is composed of energy due to its motion then its called the kinetic energy (K.E). These two energies are associated with one another.

An object when placed at a certain height, it contains the maximum amount of  P.E. and absence of K.E. As the object is allowed to move downward, the P.E starts decreasing and the K.E starts increasing. Before the point of contact (collision) between the object and the ground surface, there will be maximum K.E and no P.E in the object.  After it hits the ground, this energy gets transfer into the sound energy.

Hence, it can be concluded that when a rock bounces down a mountain, it gains its maximum amount of K.E before striking the ground surface.