A 15kg cannonball and a 1kg football are dropped to the ground from a height of 10 metres. Calculate the speed of the cannonball and of the football just before they hit the ground (you may ignore air resistance).

Aim of question: demonstrate that the speed of a dropped object is independent of its mass, and depends only on the height it is dropped from.

Solution: equate formulae for kinetic energy and for gravitational potential energy. Notice that the mass terms cancel, and rearrange to solve for speed.