Question:
Water in a rectangular reservoir having base 80 m by 60 m is 6.5m deep. In what time can the water be pumped by a pipe of which the cross-section is a square of side 20 cm if the water runs through the pipe at the rate of 15km/hr.
Solution:
Flow of water = 15 km/hr
= 15000 m/hr
Volume of water coming out of the pipe in one hour,
$\Rightarrow 20 / 100 * 20 / 100 * 15000=600 \mathrm{~m}^{3}$
Volume of the tank = 80 * 60 * 6.5
$=31200 \mathrm{~m}^{3}$
Time taken to empty the tank $=\frac{\text { Volume of tank }}{\text { Volume of water coming out of pipe in one hour }}$
= 31200/600 = 52 hours