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Water falls from a 40 m high dam at the rate of 9 × 10 4 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 )

1. 25
2. 50
3. 100
4. 18

Correct answer: 50

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