Question

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/s^2)

(a) 1.5 x 10^16 J

(b) 2.5 x 10^16 J

(c) 3.5 x 10^16 J

(d) 4.5 x 10^16 J

I have been asked this question in final exam.

I need to ask this question from Gravitational Potential Energy in chapter Gravitation of Physics – Class 11

Answer 1

Right option is (b) 2.5 x 10^16 J

Easy explanation: Mass of 50 cubic km of water = 5  x 10^13 kg; Density of water = 1 g/cubic cm

Work done = m x g x h

 = (5  x 10^13 x 10 x 50) Joules

 = 2.5 x 10^16 J.