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 $g=10m{s}^{-2}$ , 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 $=\frac{inputenergy}{time}=\frac{10^5/6}{5}=\frac{10^5}{30}=3.3kW$