Question

.75m pipe connects two reservoirs. water is pumped from the lower reservoir to a reservoir 42m higher using a 850 kw pump, ep=78%. If Head losses are 22m, define Q

Answer 1

work done per second = rho Q g h = useful power

you need more for head losses
rho Q g (h+22) = power needed , Q is in m^3/s
= 850,000 * 0.78
rho = 1000 kg/m^3
g = 9.81 m/s^2
so
1000 * Q * 9.81 (64) = 0.78 * 850,000