During the fall, all the initial potential energy of the rock
[tex]U=mgh[/tex]
has converted into kinetic energy of motion
[tex]K= \frac{1}{2}mv^2 [/tex]
where h is the initial height of the rock, m its mass, and v its velocity just before hitting the water. So, for energy conservation, we have
[tex]U=K[/tex]
and so we can find the value of K, the kinetic energy of the rock just before hitting the ground:
[tex]K=U=mgh = (12.0 kg)(9.81 m/s^2)(25.0 m)=2943 J[/tex]
