# Fluid Mechanics Questions and Answers – Most Economic Trapezoidal Section

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

1. Determine the top width length of the most economical trapezoidal channel section having depth y and side slope Z.
a) $$\sqrt{1+Z^2}$$
b) $$\frac{y}{2} \sqrt{1+Z^2}$$
c) y$$\sqrt{1+Z^2}$$
d) 2y$$\sqrt{1+Z^2}$$

Explanation:

2. Estimate the hydraulic radius of the most economical trapezoidal channel section having depth y and side slope Z.
a) y2
b) y
c) 2y
d) 3y

Explanation:

R = $$\frac{y(B+Zy)}{B+2y\sqrt{1+Z^2}} = \frac{y(B+Zy)}{B+B+2Zy} = \frac{y}{2}$$

3. The top width of a most economical trapezoidal channel section is 7m and the side slope of the channel is 1H:2V, determine the depth of the channel section.
a) 2.13m
b) 3.13m
c) 4.13m
d) 5.13m

Explanation:

4. The top width of a most economical trapezoidal channel section is 8m, determine the hydraulic radius of the channel if the side slope is 1H:3V.
a) 1.8m
b) 1.9m
c) 2.0m
d) 2.1m

Explanation:

5. The base of the most economical trapezoidal channel section is 6m and the side slope is 1H:2V, calculate the maximum discharge through the channel if the bed slope is 1 in 1000 and C = 50.
a) 120.61 m3/s
b) 110.61 m3/s
c) 100.61 m3/s
d) 90.61 m3/s

Explanation:
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6. Calculate the maximum discharge through a trapezoidal section having depth 3m, side slope 1H:4V and bed slope of 1 in 2000. Given: n = 0.025.
a) 19.09 m3/s
b) 20.09 m3/s
c) 21.09 m3/s
d) 22.09 m3/s

Explanation:

7. The wetted area of a most economical trapezoidal section is 21.58m2, base width of 5m and side slope of 1H:3V. Calculate the maximum discharge through the channel if the C=60 and S0=1/500.
a) 56.32 m3/ s
b) 66.32 m3/ s
c) 76.32 m3/ s
d) 86.32 m3/ s

Explanation:

8. Calculate the depth of the most economical trapezoidal channel section having wetted area equal to 50m2 and the side slope of 1H:5V.
a) 3.21m
b) 4.21m
c) 5.21m
d) 6.21m

Explanation:

9. The wetted perimeter of the most economical trapezoidal section is 7.47m, the base width is 3m and has the side slope of 1H:2V.
a) 1m
b) 2m
c) 3m
d) 4m

Explanation:

10. Calculate the maximum discharge through a trapezoidal channel if the wetted perimeter is 6.24m, side slope of 1H:2V and base width of 4m. Given: C=55 and S0=1/1500.
a) 3.52 m3/s
b) 4.52 m3/s
c) 5.52 m3/s
d) 6.52 m3/s

Explanation:

11. The maximum discharge through the trapezoidal channel is 20 m3/s and the velocity of flow is 5 m/s. Calculate the base width of the channel if the side slope is 1H:4V.
a) 3.31m
b) 2.31m
c) 1.31m
d) 0.31m

Explanation:

12. What is the side slope for the most economic trapezoidal channel having depth y and base width B?
a) $$\frac{1}{\sqrt{2}}$$
b) $$\frac{1}{\sqrt{3}}$$
c) $$\frac{1}{2}$$
d) $$\frac{1}{3}$$

Explanation:

13. What is the angle made by the sloping side when the trapezoidal channel discharges to the maximum extent?
a) 30°
b) 45°
c) 60°
d) 90°

Explanation:

14. Calculate the maximum discharge through a trapezoidal channel if the depth is 5m.
a) 56.67 m3/s
b) 66.67 m3/s
c) 76.67 m3/s
d) 86.67 m3/s

Explanation:

15. If the side slope angle in a trapezoidal section is 45° and it discharges to the maximize extent, calculate the top width of the channel section. Given: y = 4m
a) 10.31m
b) 11.31m
c) 12.31m
d) 13.31m

Explanation:

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