# Water a canal , 30dm wide and 12 dm deep , is flowing with a velocity of 20km per hour . how much area will it irrigate in 30 min, if 9 cm of standing water is desired ?

Solution:  Water in the canal form a cuboid of breadth = 12 dm = 12/10 m = 1.2 m ,

height =30 dm = 30/10 m = 3 m

and ,      Length = Distance covered by water in 30 minutes

= Velocity of water $\times$ time

$=20000\times\frac{30}{60}m =10000m$

$\therefore$            Volume of water flown in 30 min $=$   $lbh=(1.2\times 3 \times 10000)m^3=36000m^3$

Suppose area irrigated be $A$ $m^2.$ Then ,

$A\times \frac{9}{100}=$    Volume flown in 30 minutes.

$\Rightarrow$            $A \times \frac{9}{100}= 36000\Rightarrow A = 400000m^2$

Hence , area irrigated = 400000$m^2$

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