Question

A canal is 300 cm wide and 120 cm deep. The water in the canal is flowing with a speed of 20 km/hr. How much area will it irrigate in 20 minutes if 8 cm of standing water is desired ?

Answer 1

Width of the canal = 300 cm = 3 m
Depth of the canal = 120 cm = 1.2 m
Speed of water flow = 20 km/h = 20000 m/h
Distance covered by water in 1 hour or 60 min = 20000 m
So, distance covered by the water in 20 min = $\frac{20}{60}\times 20000=\frac{20000}{3}m$
Amount of water irrigated in 20 mintues
$=3\times 1.2\times \frac{20000}{3}=24000$ m³
Area irrigated by this water if 8 cm of standing water is desired will be
$\frac{24000}{{\displaystyle \frac{8}{100}}}=300000{\mathrm{m}}^2$

So, area irrigated will be 300000 m² or 30 hectors.