When the cannonball is shot upwards, kinetic energy converts to gravitational potential energy (GPE).
As the ball rises, speed decreases and height increases.
So when the cannonball has reached its maximum height, all of the Kinetic energy has transferred into gravitational potential energy.
(Because at the max height, the cannonball for a brief moment has no velocity, and thus no kinetic energy)
So the GPE is 48279 Joules at it's maximum height.
