A canal is 300 cm wide and 120 cm deep. The water in the canal is flowing at a speed of 20 km/h. How much area will it irrigate in 20 minutes if 8 cm of standing water is desired?
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Cross section area of canal =
300
×
120
= 36000 sq.cm
Speed of water flow = 20 km/h = 20000 m/h =
20
×
10
3
×
10
2
cm/h
=
2
×
10
6
c
m
/
h
r
Hence, in the volume of water flowing
36000
×
2
×
10
6
cubic cm:
=
7.2
×
10
10
c
c
Is to min volume of water =
7.2
×
10
10
/
60
3
×
/
30
=
2.4
×
10
10
c
c
Let the area of field being irrigated = A sq. cm.
Required studing height of water = 8 cm
∴
Volume of water in field
=
A
×
8
cc --- (2)
this must be equal to volume of water give by (1)
∴
A
×
8
=
2.4
×
10
10
A
=
2.4
8
×
10
10
s
q
.
c
m
=
3
×
10
9
s
q
.
c
m
=
3
×
10
9
10
4
s
q
.
c
m
=
3
×
10
5
s
q
.
c
m
Ans = 3×10⁵ sq.m
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