Question

Water falls from a 40 m high dam at the rate of 9 × 104 kg per hour. Fifty percentage of gravitational potential energy can be converted into electrical energy. Using this hydro electric energy number of 100 W lamps, that can be lit, is :
(Take g = 10 ms-2)

• A. 25
• B. 50
• C. 100
• D. 18

Answer 1

Answer: (B)

50

Answer 2

The correct answer is (B) : 50
Total gravitational PE of water per second
$=\frac{mgh}{T}$
$=\frac{9×10^4×10×40}{3600}=10^4$ 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