Question

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 $g=10\text{ }m{{s}^{-2}}$ )

• A. 0.6
• B. 0.4
• C. 0.2
• D. 0.3

Answer 1

Answer: (D)

0.3

Answer 2

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 $=\frac{work}{t}$
$=\frac{9\times {{10}^{5}}}{5\times 60}=3\,kW$
Hence, efficiency
$=\frac{useful\text{ }power}{consuming\text{ }power}$
$=\frac{3}{10}=30$