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A water reservoir tank of capacity 250m3 is situated at a height of 20m from the water level. What will be the power of an electric motor to be used to fill the tank in 3 hours? Efficiency of motor is 70%

Given
Volume (v)=250m3
Height (h)=20m
Time (t)=3hrs=10800sec
Efficiency of motor (η)=70%
Power of the electric motor (Pin)=?

We have, η=PinPout100% .......... (i)
 Firstly we have to find ,
Pout=Workdonetime ......... (ii)

But,
Work done to fill the tank W=mgh=ρvgh=10002501020=5107J
 [Since, density of water in SI system is 1000kg/m3]
Then from equation (ii), we get
Pout=510710800 =4.63103Watt
Finally from equation (i), we get
Pin=Poutη=4.631030.7=6614Watt
∴ Power of the electric motor (Pin)=6614Watt

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