Question

A 2 kg ball is released from rest at the top of a track and

reaches a speed of 10 m/s at the bottom.
a. How much kinetic energy does the ball have?
b. How much potential energy did it have at the top of the
hill (assuming no energy was lost)?
c. What was the height of the hill?

Answer 1

a) The formula for kinetic energy is E = 1/2 mv^2, so the energy of the ball is 1/2 * 2 * 10^2 = 100J. b) Energy is always conserved, and so if no energy is lost to resistive forces then all 100J of kinetic energy came from its potential energy at the top of the track. c) The formula for potential energy is E = mgh, which we can rearrange for h = E/mg. We know the energy, the mass and the strength of gravity, so we can find h = 100 / (2*9.81) = 5.10m.