Water falling from a 50 m high fall is to be used for generating electric energy. If 1.8 × 105 kg of water falls per hour and half the gravitational potential energy can be converted into electric energy, how many 100 W lamps can be lit?
Height from which the water falls, h = 50 m
Mass of water falling per hour = 1.8 × 105 kg
Mass of water falling per sec,
m= 50 kg
Gravitational potential energy released per sec = mgh
= 50 × 9.8 × 50
= 24500 J
Electrical energy generated per sec = (Gravitational potential energy)/2
= 24500/2
= 12250 J
Power generated = 12250 J/s or W
Number of 100 W lamps that can be lit from this power = 12250/100 = 122.5 ≈ 122 lamps