# Fluid Mechanics Questions and Answers – Gradually Varied Flow(GVF) – 5

This set of Fluid Mechanics Question Paper focuses on “Gradually Varied Flow(GVF) – 5”.

1. Specific energy in GVF changes only under which of the following conditions.
a) Difference between bed slope and slope of energy line
b) Both bed slope and energy slope are equal
c) Presence of bed slope alone
d) Presence of energy slope alone

Explanation: We know that dEdx = S0 – Sf
Hence if there’s a difference between bed slope and energy slope specific energy changes.

2. The channel is prismatic in case of a GVF.
a) True
b) False

Explanation: In a GVF a flow is steady and the channel section is uniform throughout, hence it is prismatic.

3. Calculate the value of frictional slope for a rectangular channel having width 5m and depth 3m. Given:V=2 m/s and n = 0.012.
a) 2.01×10-4
b) 3.01×10-4
c) 4.01×10-4
d) 5.01×10-4

Explanation:

Friction slope is same as slope of energy line and the same equations are applicable.

4. Calculate the frictional slope of a triangular channel having depth 2.5m and side slope of 1H:2V if the rate of change of specific energy is 1.6×10-5m/s. Given:V=1.57 m/s
a) 5.53×10-4m
b) 6.53×10-4m
c) 7.53×10-4m
d) 8.53×10-4m

Explanation:

5. What happens to the depth of flow when there is an obstruction in the path?
a) Remains the same
b) Increases
c) Decreases
d) Flow stops

Explanation: When the flow is obstructed the depth of flow increases as the water flows over the object. This change in path is called back water curve.
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6. Calculate the value of Froude’s number if the ratio of rate of change of specific energy and rate of change of depth is 0.9.
a) 0.29
b) 0.30
c) 0.31
d) 0.32

Explanation:

7. Which of the following assumptions is true in case of GVF?
a) The flow is not steady
b) The streamlines are parallel
c) Pressure distribution is not hydrostatic
d) Channel has varying alignment and shape

Explanation: The flow in a GVF is steady and hence the streamline are parallel to each other.

8. The ratio of bed slope and the slope of energy line is 2, calculate the value of slope of energy line if the length of back water curve is 20000m. Given: E1=2m and E2=5m.
a) 0.5×10-4
b) 1.0×10-4
c) 1.5×10-4
d) 2.0×10-4

Explanation:

9. The depth and widths of a trapezoidal channel section are 2m and 4m respectively and the side slope of 1H;5V, calculate the rate of change of depth if the rate of change of specific energy is 1.5×10-5. Given: S0=1 in 1000,C=35.
a) 0.5×10-5m
b) 1.0×10-5m
c) 1.5×10-5m
d) 2.0×10-5m

Explanation:

10. Calculate the head loss in a channel if the length of the back water curve is 30000m and the slope of the energy line is 4×-4.
a) 8m
b) 10m
c) 12m
d) 14m

Explanation: Consider hL = Sf L;hL = 12m.

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