# 60 most important Fluid mechanics (2) mcq questions

Q. 1. For a wide rectangular channel, the hydraulic radius is approximately equal to the ——–
—-
A : Flow depth
B : Width of channel
C : Cross-sectional area
D : Perimeter

Flow depth

Q. 2. The flow will be in the supercritical state in the following types of GVF profiles
A : All S curves
B : M2
C : A3, M3, S2
D : S2, M2, S3

A3, M3, S2

Q. 3. Identify the incorrect statement: The possible GVF profiles in
A : Mild slope channels are M1, M2, and M3
B : Adverse slopes are A2 and A3
C : Horizontal channels are H1 and H3
D : Critical slope channels are C1 and C3

Horizontal channels are H1 and H3

Q. 4. What is momentum?
A : Mass * acceleration
B : Mass * Volume
C : Mass flow rate * velocity
D : Mass flow rate* density

Mass flow rate * velocity

Q. 5. Specific force is __________ to mass flow rate.
A : Directly proportional
B : Inversely proportional
C : Independent
D : Not proportional

Directly proportional

Q. 6. A valve is suddenly closed in a water main in which the velocity is 1 m/sec and velocity of
pressure wave is 981 m/ sec. The inertia head at the valve will be

A : 1 m
B : 10 m
C : 100 m
D : 980 m

10 m

Q. 7. In hydraulic jump
A : Higher kinetic energy is dissipated
B : Higher potential energy is dissipated
C : No energy dissipation occurs
D : Energy remains constant

Higher kinetic energy is dissipated

Q. 8. In venturiflume, hydraulic jump
A : Occurs
B : Does not occur
C : Can not be predicted
D : Sometimes occur

Does not occur

Q. 9. Whan a body is placed at zero angle of incidence, the body experiences
A : Drag
B : Lift
C : Stops motion
D : Both drag and lift

Drag

Q. 10. Under which of the following condition Steady-Non uniform flow occurs in open
channel

A : When discharge and depth both vary along channel length
B : When a constant discharge flows at acontant depth of flow
C : When a constant discharge flows in a channel laid at a fixed slope
D : For a constant discharge the liquid depth varies along length of channel

For a constant discharge the liquid depth varies along length of channel

Q. 11. When drag force acts on a body the force extered by body is called
A : Friction drag
B : Shear drag
C : Resistance
D : Wave drag

Resistance

Q. 12. The strength of hydraulic jump is governed by
A : Width of flow
B : Upstream velocity
C : Downstream velocity
D : Upstream Froudee number

Upstream Froudee number

Q. 13. Boundary layer separtion is caused by
A : Boundary suction
C : Boundary layer thickness becomes zero
D : K.E of fluid reduces to zero near boundary

K.E of fluid reduces to zero near boundary

Q. 14. Flow around industry stack and chimney represnt flow around
A : Sphere
B : Cylinder
C : Airfoil
D : Flat plae

Cylinder

Q. 15. The flow in open channel is characterised as laminar when
A : Reynold no. less than 500
B : Reynold no. greater than 2000
C : Reynold no. Greater than 500 and less than 2000
D : none of these

Reynold no. less than 500

Q. 16. In hydraulic jump study the flow is assumed to be
A : Nonuniform
B : Uniform

Uniform

Q. 17. Open channel flow occurs due to
A : External force Applied
B : Gravitational force Applied due to bed slope
C : Shear strss imparted due to wind
D : Less Viscosity

Gravitational force Applied due to bed slope

Q. 18. The jet ratio is defined as the ratio of the
A : diameter of the jet to the diameter of Pelton wheel
B : velocity of jet to the velocity of Pelton wheel
C : diameter of Pelton wheel to the diameter of jet
D : velocity of Pelton wheel to the velocity of jet

diameter of Pelton wheel to the diameter of jet

Q. 19. The ratio of quantity of liquid discharged per second from the pump to the quantity of
liquid passing per second through the impeller is known as

A : Manometric efficiency
B : Mechanical efficiency
C : Overall efficiency
D : Volumetric efficiency

Volumetric efficiency

Q. 20. To discharge a large quantity of liquid by multi-stage centrifugal pump, the impellers
are connected

A : In Parallel
B : In series
C : In parallel and in series both
D : None of the above

In Parallel

Q. 21. The depth of the bucket for a Pelton wheel is generally …………… the diameter of jet.
A : equal to
B : 1.2 times
C : 1.8 times
D : double

1.2 times

Q. 22. The ratio of the power given to water at outlet of the pump to the power available at the
impeller is known as…

A : Mechanical Efficiency
B : Overall Efficiency
C : Manometric Efficiency
D : Hydraulic Efficiency

Manometric Efficiency

Q. 23. The transition from laminar flow to turbulent flow occurs when
A : Reynolds number increases
B : Reynolds number decreases
C : Reynolds number is the same
D : Froude’s number increases

Reynolds number increases

Q. 24. If pre-jump and post-jump depths are 0.4m and 1.52m respectively, then the energy lost
in hydraulic jump is

A : 0.577m
B : 0.608m
C : 3.863m
D : 2.124m

0.577m

Q. 25. In a two dimensional incompressible steady flow around an airfoil, the stream lines are
2 cm apart at a great distance from the airfoil, where the velocity is 30 m/sec. The velocity near
the airfoil, where the stream lines are 1.5 cm apart is

A : 22.5 m/sec
B : 33 m/sec
C : 40 m/sec
D : 90 m/sec

40 m/sec

Q. 26. Calculate the maximum discharge through a rectangular channel
having depth 3m, bed slope of 1 in 1000.

A : 33.85m^3/s
B : 35.85m^3/s
C : 34.85m^3/s
D : 31.85m^3/s

34.85m^3/s

Q. 27. The Froude’s number for a flow is1. What type of flow is it?
A : SubCritical
B : Super critical
C : Critical
D : Tranquil

Critical

Q. 28. In GVF, dy/dx is positive
A : K > Ko and Z > Zc
B : K > Ko and Z < Zc C : K > Ko and Zo > ZC
D : Z > K and Zc > Ko

K > Ko and Z > Zc

Q. 29. The specific speed of a hydraulic turbine depends upon
A : Speed and power developed
B : Discharge and power developed
C : Speed and head of water
D : Speed, power developed and head of water

Speed, power developed and head of water

Q. 30. With ususal notations, discharge through channel by Chezy’s formula is given by
A : Q=AxCx(RS)1/2
B : Q=AxCx Rx(S)1/2
C : Q=AxCx(R)1/2x S
D : Q=AxCxRxS

Q=AxCx(RS)1/2

Q. 31. Which of the following Power Plant causes least environmental pollution?
A : Thermal Power Plant
B : Hydro Power Plant
C : Nuclear Power Plant
D : Diesel Power Plant

Hydro Power Plant

Q. 32. The phenomenon occurring in an open channel when a rapidly flowing stream abruptly
changes to slowly flowing stream causing a distinct rise of liquid surface, is

A : Uniform flow
B : Critical discharge
C : Hydraulic jump
D : None of the these

Hydraulic jump

Q. 33. With the same cross-sectional area and immersed in same turbulent flow, the largest
total drag will be on

A : a circular disc of plate held normal to flow
B : a sphere
C : a cylinder
D : a streamlined body

a circular disc of plate held normal to flow

Q. 34. In a rectangular channel if flow area is 6m2, wetted perimetr is 6.92m ,bed slope is 1 in
181 and Manning’s constant is 0.03, then discharge of flow will be

A : 1.89 cumec
B : 2.76 cumec
C : 3.25 cumec
D : 4.37 cumec

2.76 cumec

Q. 35. Water hammer occurs in ______________.
A : Spillway
B : Penstock
C : Turbine
D : Surge Tank

Penstock

Q. 36. The ratio of the power output of the pump to the power input of the pump is known
as…

A : Mechanical Efficiency
B : Overall Efficiency
C : Manometric Efficiency
D : Hydraulic Efficiency

Overall Efficiency

Q. 37. Section factor is the product of
A : Wetted area and square root of hydraulic depth
B : Wetted perimeter and square root of hydraulic depth
C : Wetted area and hydraulic depth
D : Wetted perimeter and hydraulic depth

Wetted area and square root of hydraulic depth

Q. 38. For GVF computation in rectangular channel,the average friction slope over two
sections is 0.00034 and change in specific energy over the same two sections is 0.088 m. If bed
slope of the channel is 0.0001, compute the distance between these two sections using direct step
method formula.

A : 277.98
B : 366.67
C : 627.98
D : 400.28

366.67

Q. 39. Flow leading from a spillway or a sluice gate to a mild slope is a practical example of
…………profile

A : M1
B : M3
C : M2
D : S3

M3

Q. 40. What is the pressure in Pascals at a depth of 1 m below the water surface
A : 98100Pa
B : 980Pa
C : 98Pa
D : 1Pa

98100Pa

Q. 41. Water hammer produces a knocking sound
A : When the velocity of pressure wave = velocity of sound
B : When the velocity of pressure wave < velocity of sound C : When the velocity of pressure wave > velocity of sound
D : None

When the velocity of pressure wave = velocity of sound

Q. 42. A turbine develops 10000 kw under head of 25 meters at 135 r.p.m. Its specific speed is
A : 175.4 r.p.m.
B : 215.5 r.p.m.
C : 241.5 r.p.m.
D : 275.4 r.p.m.

175.4 r.p.m.

Q. 43. Estimate the discharge of water in a trapezoidal channel section having a depth 3m,
width of 6m, side slope of 1H:2V and velocity of water is 2m⁄s.

A : 45 cum/s
B : 40 cum/s
C : 50 cum/s
D : 55 cum/s

45 cum/s

Q. 44. Air flows at a velocity of 1 meter per second around a body having an projected area of
1.2 sq m the density of air is 1.2 kg per Cum and Cl is 0.20 the drag force developed is

A : 0.15N
B : 0.144N
C : 0.288N
D : 1.05N

0.144N

Q. 45. In a wide rectangular river the depth of flow is 3 m and has an average bed slope of
0.0005. If Manning’s n = 0.035, the critical depth = ………..m

A : 0.587
B : 1.992
C : 1.175
D : 0.857

1.175

Q. 46. A rectangular channel section has depth y andwidth B, calculate the most economical
area of the channel.

A : y^2
B : 2y^2
C : By
D : B2

2y^2

Q. 47. The maximum discharge through a rectangular channel is 7.15 m^⁄s, determine the
depth of the channel where S=1/2000 and
C=40.

A : y=1m
B : y=2m
C : y=1.5m
D : y=2.5m

y=2m

Q. 48. For a hydraulically efficient rectangular channel of bed width 4 m, the depth (m) of flow
is

A : 3
B : 1
C : 2
D : 4

2

Q. 49. Uniform flow is taking place in a rectangular channel having a longitudinal slope of
0.004 and Manning’s n 0.013. The discharge in the channel is q = 1.2 cu.m/s/m. The slope of the
channel is classified in GVF analysis as

A : mild
B : critical
C : steep
D : very steep

steep

Q. 50. A 2 m wide rectangular channel has normal depth of 1.25 m when the discharge is 8.75
cu.m/s. The slope of the channel is classified as

A : Critical
B : Steep
C : mild
D : horizontal

Critical

Q. 51. For a rectangular channel section if width and depth of channel section are 4m and 2m
respectively, and the flow depth is 1.5m, then the wetted perimeter and flow area will be

A : 8m and 10 sqm
B : 6m and 7 sqm
C : 10m and 8 sqm
D : 7m and 6 sqm

7m and 6 sqm

Q. 52. The discharge from a spillway on a horizontal floor is 8 cumecs per meter width. If the
depth before the jump is 50 cm, the depth after the jump in meters will be

A : 2.56
B : 4.86
C : 5.23
D : 4.1

4.86

Q. 53. Water hammer depends on the elastic modus of
A : Water
B : Both of water and pipe
C : pipe
D : None

Both of water and pipe

Q. 54. The type of flow in a channel with cross sectional area of 50 sq.m. and top of the channel
is 5m. The mean velocity of flow is 0.1m/s and the absolute viscosity of water 0.625 N-s/sq. m. is

A : Laminar
B : Turbulent
D : Transitional

Transitional

Q. 55. A turbine is required to develop 1500 kW at 300 r.p.m. under a head of 150 m. Which of
the following turbine should be used?

A : Pelton Wheelwith one nozzel
B : Pelton wheel with two or more nozzles
C : Kaplan turbine
D : Francis turbine

Pelton Wheelwith one nozzel

Q. 56. A Pelton wheel develops 1750 kW under a head of 100 meters while running at 200
r.p.m. and discharging 2500 liters of water per second. The unit speed of the wheel is

A : 10 r.p.m.
B : 20 r.p.m.
C : 40 r.p.m.
D : 80 r.p.m.

20 r.p.m.

Q. 57. If flow velocity is 6m/s and flow depth is 0.4m, then hydraulic jump will
A : Not occur
B : Can not be predicted
C : Occur
D : Predicted but will not occur

Occur

Q. 58. Determine slope of water surface profile w.r.t. channel bottom for the following data:
depth of flow = 0.72 m, normal depth = 1.08 m, critical depth = 0.467 m, bed slope = 1 in 2500,
Manning’s n = 0.02.

A : 00458
B : 00358
C : 001575
D : 006758

001575

Q. 59. The amount of power delivered or received at a given point at any instance is known as
B : Power factor
C : Plant Capacity

Q. 60. A rectangular channel 10 m wide carries a discharge of Q = 30 cu.m/s and it is laid at a
slope of 0.0001. If depth at two sections are 1.8 m and 1.9 m, compute the distance between the
two section if Mannings n = 0.015.

A : 629.23 m
B : 105.23 m
C : 502.23 m
D : 283.33 m