Q. An electric pump is used to fill an overhead talk of capacity $9m^{3}$ kept at a height of $10m$ above the ground. If the pump takes 5 minutes to fill the tank by consuming $10kW$ power the efficiency of the pump should be (Take $g = 10ms^{- 2}$)
A) 60%
B) 40%
C) 20%
D) 30%
Explanation
(d) Work done in raising water $= mgh$
$\therefore W =$ ( volume $\times$ density) $gh = (9 \times 1000) \times 10 \times 10$
$\Rightarrow W = 9 \times 10^{5}\ J$
$\therefore$ Useful power $= \frac{work}{time} = \frac{9 \times 10^{5}}{5 \times 60} = 3kW$
$\therefore$ Efficiency $= \frac{3}{10} = 30\%$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.