1000+ Fluid Mechanics Multiple Choice Question Answer [Solved]

1. The normal stress is same in all directions at a point in a fluid
A. Only when the fluid is frictionless
B. Only when the fluid is incompressible and has zero viscosity
C. When there is no motion of one fluid layer relative to an adjacent layer
D. Irrespective of the motion of one fluid layer relative to an adjacent layer
Answer : C

2. For pipes, laminar flow occurs when Reynolds number is
A. Less than 2000
B. Between 2000 and 4000
C. More than 4000
D. Less than 4000
Answer : A

3. The center of gravity of the volume of the liquid displaced by an immersed body is called
A. Metacentre
B. Center of pressure
C. Center of buoyancy
D. Center of gravity
Answer : C

4. Bernoulli equation deals with the law of conservation of
A. Mass
B. Momentum
C. Energy
D. Work
Answer : C

5. Kinematic viscosity is dependent upon
A. Pressure
B. Distance
C. Density
D. Flow
Answer : C

6. During the opening of a valve in a pipe line, the flow is
A. Steady
B. Unsteady
C. Uniform
D. Laminar
Answer : B

7. The weight per unit volume of a liquid at a standard temperature and pressure is called
A. Specific weight
B. Mass density
C. Specific gravity
D. None of these
Answer : A

8. According to Manning's formula, the discharge through an open channel is (where M = Manning's constant)
A. A × M × m^1/2 × i^2/3
B. A × M × m^2/3 × i^1/2
C. A^1/2 × M^2/3 × m × i
D. A^2/3 × M^1/3 × m × i
Answer : B

9. The unit of kinematic viscosity in S. I. units is
A. N-m/s
B. N-s/m²
C. m²/s
D. N-m
Answer : C

10. If the depth of water in an open channel is less than the critical depth, the flow is called
A. Critical flow
B. Turbulent flow
C. Tranquil flow
D. Torrential flow
Answer : D

11. Poise is the unit of
A. Surface tension
B. Capillarity
C. Viscosity
D. Shear stress in fluids
Answer : C

12. The bulk modulus of elasticity
A. Has the dimensions of 1/pressure
B. Increases with pressure
C. Is large when fluid is more compressible
D. Is independent of pressure and viscosity
Answer : B

13. Coefficient of discharge Cd is equal to (where Cc = Coefficient of contraction, Cv = Coefficient of velocity, and Cr = Coefficient of resistance)
A. Cc × Cv
B. Cc × Cr
C. Cv × Cr
D. Cc/Cr
Answer : A

14. Two dimensional flows occurs when
A. The direction and magnitude of the velocity at all points are identical
B. The velocity of successive fluid particles, at any point, is the same at successive periods of time
C. The magnitude and direction of the velocity do not change from point to point in the fluid
D. The fluid particles move in plane or parallel planes and the streamline patterns are identical in each plane
Answer : D

15. The tendency of a liquid surface to contract is due to the following property
A. Cohesion
B. Adhesion
C. Viscosity
D. Surface tension
Answer : D

16. The loss of head at entrance in a pipe is (where v = Velocity of liquid in the pipe)
A. v²/2g
B. 0.5v²/2g
C. 0.375v²/2g
D. 0.75v²/2g
Answer : B

17. The water pressure per metre length on a vertical masonry wall of dam is (where w = Specific weight of the liquid, and H = Height of the liquid)
A. wH/2
B. wH
C. wH²/2
D. wH²/4
Answer : C

18. Bernoulli's equation is applied to
A. Venturimeter
B. Orifice meter
C. Pitot tube
D. All of these
Answer : D

19. The discharge over a right angled notch is (where H = Height of liquid above the apex of notch)
A. (8/15) C_d. 2g. H
B. (8/15) C_d. 2g. H^3/2
C. (8/15) C_d. 2g. H²
D. (8/15) C_d. 2g. H^5/2
Answer : D

20. When the flow parameters at any given instant remain same at every point, then flow is said to be
A. Quasi-static
B. Steady state
C. Laminar
D. Uniform
Answer : D

21. The pressure intensity in kN/m2 (or kPa) at any point in a liquid is (where w = Specific weight of liquid, and h = Depth of liquid from the surface)
A. w
B. wh
C. w/h
D. h/w
Answer : B

22. Ratio of inertia force to surface Jension is known as
A. Mach number
B. Froude number
C. Reynoldss number
D. Weber's number
Answer : D

23. A uniform body 3 m long, 2 m wide and 1 m deep floats in water. If the depth of immersion is 0.6 m, then the weight of the body is
A. 3.53 kN
B. 33.3 kN
C. 35.3 kN
D. None of these
Answer : C

24. If the depth of water in an open channel is greater than the critical depth, the flow is called
A. Critical flow
B. Turbulent flow
C. Tranquil flow
D. Torrential flow
Answer : C

25. When a cylindrical vessel, containing some liquid, is rotated about its vertical axis, the liquid surface is depressed down at the axis of its rotation and rises up near the walls of the vessel on all sides. This type of flow is known as
A. Steady flow
B. Turbulent flow
C. Vortex flow
D. Uniform flow
Answer : C

26. The upper surface of a weir over which water flows is known is
A. Crest
B. Nappy
C. Sill
D. Weir top
Answer : C

27. A notch is used to measure __________ of liquids.
A. Pressure
B. Discharge
C. Velocity
D. Volume
Answer : B

28. In an internal mouthpiece, the absolute pressure head at vena contracta is __________ the atmospheric pressure head by an amount equal to height of the liquid above the vena contracta.
A. Less than
B. More than
C. Equal to
D. None of these
Answer : A

29. Flow occurring in a pipeline when a valve is being opened is
A. Steady
B. Unsteady
C. Laminar
D. Vortex
Answer : B

30. A flow in which the viscosity of fluid is dominating over the inertia force is called
A. Steady flow
B. Unsteady flow
C. Laminar flow
D. Turbulent flow
Answer : C

31. The theoretical velocity of jet at vena contracta is (where H = Head of water at vena contracta)
A. 2gH
B. H × ?(2g)
C. 2g × ?H
D. ?(2gh)
Answer : D

32. The velocity at which the flow changes from laminar flow to turbulent flow is called
A. Critical velocity
B. Velocity of approach
C. Sub-sonic velocity
D. Super-sonic velocity
Answer : A

33. The viscosity of water at 20°C is
A. One stoke
B. One centistoke
C. One poise
D. One centipoise
Answer : D

34. A flow in which __________ force is dominating over the viscosity is called turbulent flow.
A. Elastic
B. Surface tension
C. Viscous
D. Inertia
Answer : D

35. In a free nappe,
A. The pressure below the nappe is atmospheric
B. The pressure below the nappe is negative
C. The pressure above the nappe is atmospheric
D. The pressure above the nappe is negative
Answer : A

36. Cavitation is caused by
A. High velocity
B. High pressure
C. Weak material
D. Low pressure
Answer : D

37. The pressure in Pascals at a depth of 1 m below the free surface of a body of water will be equal to
A. 1 Pa
B. 91 Pa
C. 981 Pa
D. 9810 Pa
Answer : D

38. A compound pipe is required to be replaced by a new pipe. The two pipes are said to be equivalent, if
A. Length of both the pipes is same
B. Diameter of both the pipes is same
C. Loss of head and discharge of both the pipes is same
D. Loss of head and velocity of flow in both the pipes is same
Answer : C

39. The mass of 2.5 m3 of a certain liquid is 2 tonnes. Its mass density is
A. 200 kg/m³
B. 400 kg/m³
C. 600 kg/m³
D. 800 kg/m³
Answer : D

40. The celerity (velocity) of a pressure wave in a fluid is given by (where K = Bulk modulus, and ? = Density of the fluid)
A. K.?
B. K/?
C. ?/K
D. None of these
Answer : B

41. According to Bazin's formula, the discharge over a rectangular weir is mL2g x H^3/2where m is equal to
A. 0.405 + (0.003/H)
B. 0.003 + (0.405/H)
C. 0.405 + (H/0.003)
D. 0.003 + (H/0.405)
Answer : A

42. Choose the wrong statement
A. Viscosity of a fluid is that property which determines the amount of its resistance to a shearing force
B. Viscosity is due primarily to interaction between fluid molecules
C. Viscosity of liquids decreases with increase in temperature
D. Viscosity of liquids is appreciably affected by change in pressure
Answer : D

43. The critical depth meter is used to measure
A. Velocity of flow in an open channel
B. Depth of flow in an open channel
C. Hydraulic jump
D. Depth of channel
Answer : C

44. In an internal mouthpiece, if the jet after contraction does not touch the sides of the mouthpiece, then the mouthpiece is said to be
A. Running full
B. Running free
C. Partially running full
D. Partially running free
Answer : B

45. The most economical section of a rectangular channel is one which has hydraulic mean depth or hydraulic radius equal to
A. Half the depth
B. Half the breadth
C. Twice the depth
D. Twice the breadth
Answer : A

46. An error of 1% in measuring head over the apex of the notch (H) will produce an error of _________ in discharge over a triangular notch.
A. 1 %
B. 1.5 %
C. 2 %
D. 2.5 %
Answer : D

47. Which of the following meters is not associated with viscosity?
A. Red wood
B. Say bolt
C. Engler
D. Orsat
Answer : D

48. Mercury is often used in barometer because
A. It is the best liquid
B. The height of barometer will be less
C. Its vapour pressure is so low that it may be neglected
D. Both (B) and (C)
Answer : D

49. Which of the following is an example of laminar flow?
A. Underground flow
B. Flow past tiny bodies
C. Flow of oil in measuring instruments
D. All of these
Answer : D

50. The speed of sound in a ideal gas varies directly as its
A. Absolute temperature
B. Temperature
C. Density
D. Modulus of elasticity
Answer : A