Question

Can anyone tell me how to figure out this problem? If you roll a 50 kg ball down a 25 m hill, how fast will be rolling when it gets to the bottom?

Answer 1

Potential and kinetic energies are very very fundamental ideas in physics. Even more fundamental is conservation of energy: if we assume that the energy of the ball stays in the ball (instead of going into heating/deforming the ball or ramp through friction) then the final energy of the ball is equal to the initial energy of the ball. However, initially the ball has only potential energy and finally the ball only has kinetic energy. Since the energies are the same, look at the equations for the two and equate them: mgh = (1/2)mv^2