Question

Water in a canal, 4 m wide and 15 m deep is flowing with the speed of 12 km/h. Then the area of field it will irrigate in 20 minutes, if 10 cm of standing water is required for irrigation, is

• A. $4000000m^2$
• B. $2400000m^2$
• C. $2500000m^2$
• D. $5000000m^2$

Answer 1

The correct option is B $2400000m^2$

Given that the speed of water flowing is 12 km/h.

In m/s, speed $=12\times \frac{1000}{60\times 60}m/s$

$=\frac{10}{3}m/s$

Area of the canal $=4\times 15m^2$

$\therefore$ Rate of volume flow $=(4\times 15\times \frac{10}{3})m^3/s$

= 4 × 5 × 10

= 20 × 10

$=200m^3/s$

Volume of water flowing in 20 mins = 200 × 20 × 60 (∵ 20 min = 20 × 60 sec)

$=2400000m^3$

Given that 10 cm of the standing water is required for irrigation.

∴ Area of field irrigated $=\frac{240000}{0.1}{m}^2$ (∵ 10 cm = 0.1 m)

$=2400000m^2$

Hence, the correct answer is option (b).