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Question
Water in a canal, 5·4 m wide and 1·8 m deep, is flowing with a speed of 25 km/hour. How much area can it irrigate in 40 minutes, if 10 cm of standing water is required for irrigation?
Solution
Width of the canal = 5.4 m
Depth of the canal = 1.8 m
Height of the standing water needed for irrigation = 10 cm = 0.1 m
Speed of the flowing water = 25 km/h = `25000/60=1250/3` m/min
Volume of water flowing out of the canal in 1 min
= Area of opening of canal x `1250/3`
`= 5.4 xx 1.8 xx 1250/3`
=4050 m3
∴ Volume of water flowing out of the canal in 40 min = 40 × 4050 m3 = 162000 m3
Now,
Area of irrigation = `"Volume of water flowing out from canal in 40 min"/"Height of the standing water needed for irrigation"`
`= 162000/0.1`
`= 1620000 m^2`
= 162 hectare (∵ 1 hectare = 10000 m2)
Thus, the area irrigated in 40 minutes is 162 hectare.
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