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Question
How long should an electric motor, of power 2 H.P. operate, so as to pump 5 m3 of water from a depth of 15m. [Take g = 10 N kg−1]
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Solution
Mass of water = v × d = 5m3 × 1000 kg m−3 = 5000 kg.
Height = 15 m, t = ?, g = 10 N kg−1
P = 2 H.P. = 2 × 750 = 1500 W
Work done in operating electric motor = P × t = 1500 W × t
Work done in raising water = mgh = 5000 × 10 × 15 = 750000 J
1500 × t = 750000 J
t = 500 seconds.
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