Question

Water in a canal, $30dm$ wide and $12dm$ deep is flowing with velocity of $10km/hr$. How much area will it irrigate in $30$ minutes, if $8cm$ of standing water is required for irrigation?

Answer 1

We have,
Width of the canal$=30dm=300cm=3m$
Depth of the canal$=12dm=120cm=1.2m$

It is given that the water is flowing with a velocity $10km/hr$.

Therefore length of the water column formed in $\frac{1}{2}hour=5km=5000m$

volume of the water flowing in $\frac{1}{2}hour$

= Volume of the cuboid of length $5000m$, width $3m$ and depth $1.2m$

Volume of the water following in $\frac{1}{2}hour$

$=5000\times 3\times 1.2m^3=18000m^3$

Suppose $x$ $m^2$ area is irrigated in $\frac{1}{2}$ hour. Then
$x\times \frac{8}{100}=18000$

$\Rightarrow x=225000m^2$