Question

An engine pumps up $100kg$ of water through a height of $10m$ in $5s$ . Given that the efficiency of the engine is $60\%$ . If $g=10ms^{- 2}$ , the power of the engine is:

• A. $3.3kW$
• B. $0.33kW$
• C. $0.033kW$
• D. $33kW$

Answer 1

Answer: (A)

Work output of engine $=mgh$
$=100\times 10\times 10=10^{4}J$
Efficiency $\left(\eta\right)=\frac{output}{input}$
$\therefore $ Input energy $=\frac{output}{\eta}$
$=\frac{10^{4}}{60}\times 100=\frac{10^{5}}{6}J$
$\therefore $ Power $=\frac{input energy}{time}=\frac{10^{5} / 6}{5}=\frac{10^{5}}{30}=3.3kW$