# Fluid Mechanics Questions and Answers – Most Economic Circular Section – 3

This set of Tough Fluid Mechanics Questions and Answers focuses on “Most Economic Circular Section – 3”.

1. Which of the following conditions is taken into account in case of most economical circular channel section?
a) Minimum wetted perimeter
b) Minimum wetted area
c) Maximum velocity
d) Maximum depth

Explanation: In case of a circular channel the depth continuously varies, hence the wetted area and wetted perimeter changes. Therefore the condition of maximum velocity is taken under consideration.

2. What is the condition for maximum velocity in case of most economical circular section?
a) sin⁡ 2θ=2θ
b) cos⁡ 2θ=2θ
c) tan⁡ 2θ=2θ
d) sec⁡ 2θ=2θ

Explanation:

3. What is the value of the θ in case of most economical circular channel section?
a) 128°45′
b) 129°45′
c) 130°45′
d) 131°45′

Explanation: tan⁡ 2θ=2θ where θ= 128°45.

4. What is the depth of flow in case most economical circular section considering maximum velocity?
a) 0.61D
b) 0.71D
c) 0.81D
d) 0.91D

Explanation:

5. Determine the depth of flow in case of maximum velocity when the radius of the channel is 2.2m.
a) 3.56m
b) 4.56m
c) 5.56m
d) 6.56m

Explanation: Depth = 0.81D = 0.81(4.4) = 3.56m.

6. The maximum discharge through a most economical circular section in case of maximum velocity is 0.16 m3/s calculate the bed slope of the channel if the radius is 0.4m and C = 55.
a) 1 in 1000
b) 1 in 1100
c) 1 in 1200
d) 1 in 1300

Explanation:

7. The maximum discharge through a circular channel is 0.38 m3/s and the radius of the channel is 0.6m. Calculate the value of C if S0=1 in 1000.
a) 45
b) 50
c) 55
d) 60

Explanation:

8. The maximum discharge through a circular channel is 0.61 m3/s and the radius of the section is 0.7m. Calculate the value of n if the bed slope value is 1 in 1100.
a) 0.018
b) 0.019
c) 0.020
d) 0.021

Explanation:

9. Calculate the hydraulic mean depth in case of maximum mean velocity if the radius of the channel is 0.5m.
a) 0.3m
b) 0.4m
c) 0.5m
d) 0.6m

Explanation: R = 0.3D = 0.3(1) = 0.3m.

10. Calculate the depth in case of circular channel discharging to the maximum extent if the radius of the channel is 2m.
a) 1.8m
b) 2.8m
c) 3.8m
d) 4.8m

Explanation: Depth = 0.95D = 0.95(4) = 3.8m.

Sanfoundry Global Education & Learning Series – Fluid Mechanics.

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