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Question
A hydroelectric power station takes its water from a lake whose water level is 50 m above the turbine. Assuming an overall efficiency of 40%, calculate the mass of water which must flow through the turbine each second to produce power output of 1 MW. (Take g = 10 m s−2).
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Solution
Height h = 50 m, g = 10 ms−2
Power out put = 1 MW = 106 J/S
But this is only 40 %
∴ P.E. required = `100/40 xx 1000000`
= m × 10 × 50
= 2500000
Mass of water = m = `2500000/500`
= 5000 kg
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