(a) Potential energy is high, this is because the cart is at the highest point possible.
(b) The potential energy is transferred into kinetic energy by going down the track,
(c) Potential energy is at a minimum and the kinetic energy is at the highest causing the cart to start going back up to the highest point.
(d) The cart is again at the highest point, having the highest possible potential energy and no kinetic energy.
