Compare the potential energy of a 20 kg rock on the edge of 100 m cliff with that of a 20 kg rock perched on the edge of a 50 m cliff.

The equation that gives the potential energy of an object is given by:

where 
m is the mass of the object
g is the gravitational acceleration
h is the height above the ground

Using this equation, the potential energy of the first rock is:

while the potential energy of the second rock is:


So, the potential energy of the first rock is twice that of the second rock.