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. $39\%$
• B. $69\%$
• C. $93\%$
• D. $96\%$

Answer 1

Answer: (B)

Power consumed by the motor = $5kW$
$=5\times 10^{3} \, W$
$=5000 \, W$
Power used in lifting the water
$=\frac{m g h}{t}$
$=75\times 9.8\times 4.7$
$=3454.5 \, kW$
Efficiency $=\frac{P o w e r \, u s e d}{P o w e r \, c o n s u m e d}\times 100\%$
$=\frac{3454.5}{5000}\times 100=69\%$