So I know that given a unchanging hill, and same mass between a sphere and cube, that the cube should slide down the hill faster (assuming negligible friction). This is observed through the energy "lost" by the sphere which instead of having all of its potential energy transferred towards rolling down the hill, some goes to giving the ball rotation. Now I was wondering if there is anyway to calculate of how fast a ball would roll down a hill, only given gravity. For example, a solid sphere (weighing 1kg with a radius of 1m) is on top of a hill that is 15m high with an slope of 30 degrees. How long will it take for the sphere to reach the bottom. Since this is an example problem an explanation is more helpful than an answer. Thanks!