*A cart slides down an inclined plane starting with velocity=0 at the highest point. At this point the kinetic energy is maximum.
*The cart continues sliding down. When it gets to the bottom of the hill, it crashes with wall and stops. At the moment of the crash the kinetic energy is minimum
*Now before the cart crashes with the wall, we add a spring that pushes the cart back up the hill. The cart is able to go back up because the spring transmits its potential energy to the cart.