An engine pumps 400 kg of water through height of 10 m in 40 s. Find the power of the engine if its efficiency is 80% (Take ,g =10 `ms^(-2)`).

Explanation

Work done by engine against gravity
`W=mgh=400xx10xx10=40 kJ`
Power used by engine (output power)`=(W)/(Deltat)`
`=(40xx10^(3))/(40)W=1 kW`
If power of the engine is P (input power), then
`eta=("Output power")/("Input power")`
`P=(1 kw)/(80%)impliesP=(1000xx100)/(80)W`
or `" " (100)/(80)kW=1.25 kW`