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