Question

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

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

Answer 1

Answer: (B)

Power consumed by the motor = $5kW$
$=5\times 10^{3}W$
$=5000W$
Power used in lifting the water
$=\frac{mgh}{t}$
$=75\times 9.8\times 4.7$
$=3454.5kW$
Efficiency $=\frac{Powerused}{Powerconsumed}\times 100\%$
$=\frac{3454.5}{5000}\times 100=69\%$