A child and sled with a combined mass of 55.0 kg slide down a frictionless hill that is 7.28 m high. If the sled starts from rest, what is its speed at the bottom of the hill?

Answer 1

The potential energy at the top of the hill is given by PE = mgh where m = mass, g = gravitation acceleration, h = height of hill. PE = 55.0 kg x 9.8 m/s^2 x 7.28 m = 3924 joules. Since the hill is frictionless, the kinetic energy at the bottom of the hill is equal to the PE calculated. KE = 1/2 x 55.0 kg x V^2 = 3924 joules. The only unknown is V. V = 11.9 m/s.