Question

Water falls from a 40 m high dam at the rate of $9 \times 10^4$ kg per hour. Fifty percentage of gravitational potential energy can be converted into electrical energy. Using this hydroelectric energy number of 100 W lamps, that can be lit, is: (Take g=10ms-2)

• A. 25
• B. 50
• C. 100
• D. 18

Answer 1

Answer: (B)

50

Answer 2

Total gravitational PE of water per second
=$\frac{mgh}{T}$
=$\frac{9×10^4×10×40}{3600}$=104 J/sec

50% of this energy can be converted into electrical energy so total electrical energy
=$\frac{10^4}{2}$=5000 W

So, total bulbs lit can be
=$\frac{5000 W}{100 W}$
= 50 bulbs

$\therefore ,$ The correct option is (B): 50