Question

An installation consisting of an electric motor driving a water pump left $75\, L$ of water per second to a height of $4.7\, m$. If the motor consumes a power of $5\, kW$, then the efficiency of the installation is

• A. 0.39
• B. 0.69
• C. 0.93
• D. 0.96

Answer 1

Answer: (B)

0.69

Answer 2

Power consumed by the motor $=5\, kW$
$=5 \times 10^{3} W$
$=5000\, W$
Power used in lifting the water
$-\frac{m g h}{t}$
$=7.5 \times 9.8 \times 4.7$
$=3454.5\, kW$
Efficiency $= \frac{\text { Power used }}{\text { Power consumed }} \times 100 \%$
$=\frac{3454.5}{5000} \times 100=69 \%$