Water in a canal, 6 m wide and 1.5 m deep, is flowing with a speed of 10 km/h. How much area will it irrigate in 30 minutes, if 8 cm of standing water is needed?

Area of cross-section = 6 × 1.5

= 9 m²

Speed of water = 10 km/h

Water flows through canal in 60 min = 10 km
Water flows through canal in 1 min = 
Water flows through canal in 30 min = 
= 5 km 
= 5000 m
Hence length of the canal is 5000 m.
The volume of canal = L × B × H
= (5000 × 6 × 1.5) 
= 45000 m³

Let the irrigated area be A.

Now, we know that,

The volume of water irrigating the required area will be equal to the volume of water that flowed in 30 minutes from the canal.

Vol. of water flowing in 30 minutes from canal = Vol. of water irrigating the reqd. area

⇒ 45000 = Area × height
Given height = 8 cm = 0.08 m
⇒ 45000 = Area × 0.08

Area = 562500 m²