Water fall from a $40\,m$ high dam at the rate of $9 \times 10^{4}\,kg$ 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 $\left.g=10\,ms ^{-2}\right)$
A$25$
B$50$
C$100$
D$18$
JEE MAIN 2022, Medium
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B$50$
b $\frac{9 \times 10^{4} \times g \times 40}{3600} \times 0.5= n \times 100$
$\frac{10^{4} \times 0.5}{100}= n$
$100 \times 0.5= n$
$n =50$
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