Question

A overhead tank of capacity 1000 liter has to be filled in $\frac{1}{2}$hour using water pump. Tank is kept at a height 10 m above ground and water level is 10 m below ground. The opening of inlet pipe inside tank is 1.11 cm². Assuming the efficiency of motor to be 60%, the electric power used is (Neglect viscosity) –

• A. 118 W
• B. 130 W
• C. 146 W
• D. 198 W

Answer 1

Answer: (D)

198 W

Answer 2

Volume rate of water filling tank :

Av = $\frac{1000 \times 10^{–3}}{1800}$ Ž v = 5 m/s

\ work done by pump in filling the tank

W = mgh + $\frac{1}{2}$mv²

[m = 1000 kg, h = 20 m, v = 5 m/s]

= 2.125 × 10⁵

\ P = $\frac{2.125 \times 10^{5}}{1800}$W

\ Electric power used = $\frac{10}{6} \times P$ = 198 W