A 5.45 kg rock falls from a cliff that is 23.5 m above the ground to a cliff that is 12.3 m above the ground. Find the kinetic energy of the rock when it reaches the lower cliff. Assume air does no work on the rock. What is the rock’s speed when it reaches the lower cliff? Knowns Knowns Unknowns

m = g = GPEi = ? GPEf = ?

h1 = vi = KEf = ? vf = ?

h2 = KEi =

Solve for the Unknowns

a. Determine initial height of the rock relative to the lower cliff
b. Determine the rock’s GPEi. Set the reference level as the lower cliff.
c. Identify when KE and GPE are zero
d. Use the law of conservation of energy to determine KEf
e. Determine the speed of the rock, using the equation for kinetic energy