Question

An electric pump is used to fill a tank of capacity $8m^3$ kept at the height of $20m$ from the ground. The pump takes $400$ seconds to fill the tank by consuming $5kW$. The efficiency of pump is

• A. $60$%
• B. $30$%
• C. $80$%
• D. $40$%

Answer 1

The correct option is C $80$%

The work done in filling the tank is = the increase in Potential energy.

increase in $PE=mgh.$

$m=Volume\left(V\right)\times density\left(\rho \right)$

for water, $\rho =1000kg/m^3$

$\therefore m=8000kg$

On earth, $g=9.8m/s^2$

$\therefore PE=8000\times 9.8\times 20$ $Joules$

Energy spent by pump=power$\times$time= $400\times 5000$

% efficiency = $\frac{work.done\times 100}{energy.spent}$

$=\frac{8000\times 9.8\times 20\times 100}{400\times 5000}$

$approx=80$ %