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)

$69$%

Power consumed by motor$5kW=5\times {10}^{3}W=5000W$

power used i lifting water = $\frac{mgh}{t}=7.5\times 9.8\times 4.7=3454.5W$

Efficiency = $\frac{\text{Power used}}{\text{Power consumed}}\times 100$% = $\frac{3454.5}{5000}\times 100$% = 69 %