Work Energy Power

JEE Main level, single correct, medium

86 of 183

Question 86 of 183

Water falls from a 40m40m high dam at the rate of 9×104kg9\times {10}^{4}kg per hour. Fifty percentage of gravitational potential energy can be converted into electrical energy. Using this hydro electric energy number of 100W100W lamps, that can be lit, is
(Take g=10ms−2g=10{ms}^{-2})

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Answer: (B) 5050

Since 5050% efficiency is given, half of the energy of the falling water will be used by the bulbs. Therefore,
12∆mghΔt=n×P⇒12×9×1043600×10×40=100n⇒n=50\dfrac{1}{2}\dfrac{∆mgh}{\Delta t}=n\times P\Rightarrow \dfrac{1}{2}\times \dfrac{9\times {10}^{4}}{3600}\times 10\times 40=100n\Rightarrow n=50

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