We have area A = 1 sq. km = 1000 m x 1000 m
= 106m2
d = 25 mm = 25 × 10-3m
Volume of water collected due to rainfall = A.d = 25 × 103m3
Mass of water = Volume x density
= 25 x 106 kg
Fore applied to raise water = F = mg = 25 x 107 N
Distance moved = h = 1 km = 103 m
∴ Work done = Fh = 25 × 107 × 103 = 2.5 x 1011 J