According to Sir Isaac Newtons third law of motion, "For every action force, there is an equal reaction force in the opposite direction." What this means is when you exert a force upon the wall, as the ball does when it strikes it, the wall exerts an equal force back upon the ball, causing the ball to bounce back in ...
When you throw a ball against a wall or drop it onto the floor, you notice that it bounces back up again. In the same way, when the ball hits the floor and gets squished, it pushes back against the floor to try to make itself round again.
If the initial PE is mgh(initial) and the final PE is mgh(final) then mgh(initial)-mgh(final) should give you your change in PE. So, without conversions your answer should be [(.08)(9.8)(8)]-[(.08)(9.8)(6)]=change in PE which is 1.568Joules.
