A dam produces electricity from the gravitational potential energy of the water stored in it. The same dam has 50 cubic km of water stored 50 meters above the ground. What is the work done by gravity relative to the ground? (Assume g = 10 m/s²)

2.5 x 10¹⁶ J

Mass of 50 cubic km of water = 5 x 10¹³ kg;

Density of water = 1 g/cubic cm

Work done = m x g x h

   = (5 x 10¹³ x 10 x 50) Joules

   = 2.5 x 1016 J.