# Fluid Mechanics Questions and Answers – Most Economic Rectangular Section

This set of Fluid Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Most Economic Rectangular Section”.

1. For a channel to be economic which of the following parameters should be minimum.
a) Wetted perimeter
b) Wetted area
c) Section factor
d) Hydraulic depth

Explanation: If the wetted perimeter is minimum, amount of materials required for construction of the channel is less and hence the channel is more economical.

2. A rectangular channel section has depth y and width B, calculate the most economical area of the channel.
a) 2y2
b) y2
c) By
d) B2

Explanation:

3. The depth and widths of a rectangular channel section are y and B respectively, determine the economical perimeter of the section.
a) y
b) 2y
c) 3y
d) 4y

Explanation:

4. Calculate the hydraulic radius for the most economical rectangular section having depth y and width B.
a) y/2
b) y
c) 2y
d) 3y

Explanation:

5. Calculate the maximum discharge through a rectangular channel having depth 3m, bed slope of 1 in 1000.
a) 33.85m3/s
b) 34.85m3/s
c) 35.85m3/s
d) 36.85m3/s

Explanation:

6. Calculate the maximum discharge through a rectangular channel having width of 5m, bed slope of 1 in 500 and manning’s co efficient is 0.020.
a) 33.43m3⁄s
b) 32.43m3⁄s
c) 31.43m3⁄s
d) 30.43m3⁄s

Explanation:

7. The maximum discharge through a rectangular channel is 7.15m3⁄s, determine the depth of the channel where S0 = 1/2000 and C=40.
a) 4m
b) 3m
c) 2m
d) 1m

Explanation:

8. The base width of a most economical rectangular channel is 8m, calculate the hydraulic radius of the channel,
a) 5m
b) 4m
c) 3m
d) 2m

Explanation: B = 2y; y = 4m
R = y/2 = 2m.

9. Calculate the section factor for the most economical rectangular section having depth of 4m.
a) 32
b) 64
c) 128
d) 256

Explanation: Z = A√D = 2y2 √y = 2y5/2
Z = 64.

10. The ratio between maximum discharge and top width of a rectangular channel is 91:50, calculate the depth of the channel if the bed slope is 1 in 3000 and C = 50.
a) 2m
b) 3m
c) 4m
d) 5m

Explanation:

11. The ratio between normal discharge and maximum discharge through a rectangular channel is 32:6, calculate the depth of the channel if the width of the channel is 4m and bed slope, chezy’s constant remains same.
a) 1m
b) 2m
c) 3m
d) 4m

Explanation:

12. The hydraulic radius of an economical rectangular section is 4m, calculate the discharge through the channel if the bed slope of the channel is 1 in 1000 and manning’s co efficient is 0.015.
a) 680m3⁄s
b) 690m3⁄s
c) 700m3⁄s
d) 710 m3⁄s

Explanation:

Sanfoundry Global Education & Learning Series – Fluid Mechanics.

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