This is one of the important question from the cbse board exam point of view because in 2017 cbse board exam this question was asked. Question number 26 from RS Aggarwal book page number 811, exercise 17B, chapter volume and surface area of solid.

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# Water in a canal, 5.4 m wide and 1.8 m deep, is flowing with a speed of 25 km/hr. How much area can it irrigate in 40 minutes, if 10 cm of standing water is required for irrigation?

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given data,

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 ×1250/3

= 5. 4 ×1. 8 ×1250/3

= 4050 m³

∴ Volume of water flowing out of the canal in 40 min = 40 × 4050 m³

= 162000 m³

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 m²

∴ the area irrigated in 40 minutes is 1620000 m²