A motor can pump up water to fill a tank of volume 500m^3 in 25 minutes , which is placed at a height of 20m. If efficiency of the motor is 40%, calculate the power of the motor.

From the given information we can easily calculate the work done by the pump in 25 minutes
                                                                        W= mgh 
 
m is the mass of the water pumped by the motor = volume x density
                                                                         = 500 x 1= 500 kg
                                                  W= 500 x 10 x 20    ( g = 10 m/s<sup>2
                                                                      = 100000 joule

Power of the pump $\frac{W}{t}=\frac{100000}{25\times 60}=66.7 watt$

As the efficiency of the motor is 40% this means that the motor will convert only
                                                                                                                     $$\begin{gathered} \frac{40}{100}th part of of the total energy E \\ \Rightarrow 66.7=\frac{40}{100}\times E \\ \Rightarrow E=\frac{667}{4}=166.75 J \end{gathered}$$</sup>