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

The Correct Option is B

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