JEE Main · 2022 · 28 Jun 2022 · Shift 2 · Work, Power & Energy

Water fall from a 40 m high dam at the rate of

9 \times 1 0^{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 = 10 ms^{- 2}

)

(A)25
(B)50✓ Correct
(C)100
(D)18

Answer: (B)

Solution

Power from falling water =

\frac{m g h}{t} = \frac{9 \times 1 0 ^{4} \times 10 \times 40}{3600}

W. With 50% efficiency, electrical power =

0.5 \times \frac{9 \times 1 0 ^{4} \times 400}{3600} = 5000

W. Number of 100 W lamps =

\frac{5000}{100} = 50

JEE Main · 2022 · 28 Jun 2022 · Shift 2 · Single correct option

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