Question

2. Calculate the time for which a motor pump of 10 HP and efficiency 80% must be switched on, so
as to pump 20 metre cube of water through a vertical height of 20 m. [Density of water = 1000 kg m cube
g= 10 m/s square; 1 HP = 750 W]
(answer 666.67 second)​

Answer 1

Given :

Efficiency of the pump = 80%

The height of water to be raised = 20 m

Volume of water = 20 m³

To Find:

The time required for the water to reach the  height

Solution :

• Power deliverd by pump in t seconds = 10×0.8×750×t ……Equation(1)

• Potential energy of water = mgh

                                        = 20×10⁻⁶×1000×9.8×20

                                        = 3.920 J ……Equation(2)

• By equating both the equations we get

            6000×t  =  3.920

            t = 0.653 ms

The time required for the water to reach the  height Is 0.653 ms.