Question:
Water in a canal 1.5 m wide and 6 m deep is flowing with a speed of 10km/hr. How much area will it irrigate in 30 minutes if 8 cm of standing water is desired?
Solution:
The canal is 1.5 m wide and 6 m deep. The water is flowing in the canal at 10 km/hr. Hence, in 30 minutes, the length of the flowing standing water is
$=10 \times \frac{30}{60} \mathrm{~km}$
$=5 \mathrm{~km}$
$=5000 \mathrm{~m}$
Therefore, the volume of the flowing water in 30 min is
$V_{1}=5000 \times 1.5 \times 6 \mathrm{~m}^{3}$
Thus, the irrigated area in 30 min of 8 cm=0.08 m standing water is
$=\frac{5000 \times 1.5 \times 6}{0.08}$
$=562500 \mathrm{~m}^{2}$