Self-Check Potential Energy

Self-Check:	A ball thrown straight up will have the same speed on impact with the ground as a ball thrown straight down at the same speed. How can this be explained using potential energy?
Answer:	Both balls start from the same height and end at the same height, so they have the same Dy. This implies that their losses in potential energy are the same, so they must both have gained the same amount of kinetic energy.