Final answer:
When a ball is thrown upwards, it initially has kinetic energy which decreases as it rises and is converted into potential energy. As the ball falls back down, the potential energy is converted back into kinetic energy.
Step-by-step explanation:
When a ball is thrown upwards, it has a store of kinetic energy. As the ball rises, its kinetic energy decreases because it is moving against gravity and will eventually come to a stop at its highest point. At this point, the ball has reached its maximum potential energy. As the ball falls back down, its potential energy is converted back into kinetic energy, and its kinetic energy increases again as it picks up speed. When the ball hits the ground, its kinetic energy is at its maximum, and all of its potential energy has been converted back into kinetic energy.