1000+ Fluid Mechanics Multiple Choice Question Answer [Solved]

1. The critical depth for a channel is given by (where q = Unit discharge (discharge per unit width) through the channel)
A. (q/g)^1/2
B. (q²/g)^1/3
C. (q³/g)^1/4
D. (q?/g)^1/5
Answer : B

2. 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

3. For a perfect incompressible liquid, flowing in a continuous stream, the total energy of a particle remains the same, while the particle moves from one point to another. This statement is called
A. Continuity equation
B. Bernoulli's equation
C. Pascal's law
D. Archimedess principle
Answer : B

4. The total energy of each particle at various places in the case of perfect incompressible fluid flowing in continuous stream
A. Keeps on increasing
B. Keeps on decreasing
C. Remain constant
D. May increase/decrease
Answer : C

5. Which of the following is the unit of kinematic viscosity?
A. Pascal
B. Poise
C. Stoke
D. Faraday
Answer : C

6. Stoke is the unit of
A. Kinematic viscosity in C. G. S. units
B. Kinematic viscosity in M. K. S. units
C. Dynamic viscosity in M. K. S. units
D. Dynamic viscosity in S. I. units
Answer : A

7. The ratio of the inertia force to the __________ is called Euler's number.
A. Pressure force
B. Elastic force
C. Surface tension force
D. Viscous force
Answer : A

8. The highest efficiency is obtained with a channel of __________ section.
A. Circular
B. Square
C. Rectangular
D. Trapezoidal
Answer : D

9. Rain drops are spherical because of
A. Viscosity
B. Air resistance
C. Surface tension forces
D. Atmospheric pressure
Answer : C

10. The viscosity of water is __________ than that of mercury.
A. Higher
B. Lower
C. Same as
D. None of these
Answer : A

11. In a depressed 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 : B

12. In a footstep bearing, if the radius of the shaft is doubled, then the torque required to overcome the viscous resistance will be
A. Double
B. Four times
C. Eight times
D. Sixteen times
Answer : D

13. The rise of liquid along the walls of a revolving cylinder about the initial level is __________ the depression of the liquid at the axis of rotation.
A. Same as
B. Less than
C. More than
D. None of these
Answer : A

14. For manometer, a better liquid combination is one having
A. Higher surface tension
B. Lower surface tension
C. Surface tension is no criterion
D. High density and viscosity
Answer : A

15. Barometer is used to measure
A. Pressure in pipes, channels etc.
B. Atmospheric pressure
C. Very low pressure
D. Difference of pressure between two points
Answer : B

16. The discharge through a wholly drowned orifice is given by (where H1 = Height of water (on the upstream side) above the top of the orifice, H2 = Height of water (on the downstream side) above the bottom of the orifice, and H = Difference between two water levels on either side of the orifice)
A. Q = C_d × bH? × ?(2gh)
B. Q = C_d × bH₂ × ?(2gh)
C. Q = C_d × b (H₂ - H₁) × ?(2gh)
D. Q = C_d × bH × ?(2gh)
Answer : C

17. Choose the wrong statement
A. Fluids are capable of flowing
B. Fluids conform to the shape of the containing vessels
C. When in equilibrium, fluids cannot sustain tangential forces
D. When in equilibrium, fluids can sustain shear forces
Answer : D

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

19. When the Mach number is between __________ the flow is called super-sonic flow.
A. 1 and 2.5
B. 2.5 and 4
C. 4 and 6
D. 1 and 6
Answer : D

20. At the center line of a pipe flowing under pressure where the velocity gradient is zero, the shear stress will be
A. Minimum
B. Maximum
C. Zero
D. Could be any value
Answer : D

21. When a cylindrical vessel containing liquid is revolved about its vertical axis at a constant angular velocity, the pressure
A. Varies as the square of the radial distance
B. Increases linearly as its radial distance
C. Increases as the square of the radial distance
D. Decreases as the square of the radial distance
Answer : A

22. A piece of metal of specific gravity 7 floats in mercury of specific gravity 13.6. What fraction of its volume is under mercury?
A. 0.5
B. 0.4
C. 0.515
D. 0.5
Answer : C

23. The velocity corresponding to Reynold number of 2000 is called
A. Sub-sonic velocity
B. Super-sonic velocity
C. Lower critical velocity
D. Higher critical velocity
Answer : C

24. The hydraulic mean depth or the hydraulic radius is the ratio of
A. Area of flow and wetted perimeter
B. Wetted perimeter and diameter of pipe
C. Velocity of flow and area of flow
D. None of these
Answer : A

25. The discharge over a rectangular notch is (where b = Width of notch, and H = Height of liquid, above the sill of the notch)
A. (2/3) C_d × b × ?(2gH)
B. (2/3) C_d × b × ?(2g) × H
C. (2/3) C_d × b × ?(2g) × H^3/2
D. (2/3) C_d × b × ?(2g) × H²
Answer : C

26. Which of the following instruments is used to measure flow on the application of Bernoulli's theorem?
A. Venturimeter
B. Orifice plate
C. Nozzle
D. All of the above
Answer : D

27. The body will float if the force of buoyancy is __________ the weight of the liquid displaced.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : C

28. The value of mass density in kg-sec-V-m? for water at 0°C is
A. 1
B. 1000
C. 100
D. 101.9
Answer : D

29. The surface tension of mercury at normal temperature is __________ that of water.
A. Same as
B. Lower than
C. Higher than
D. None of these
Answer : C

30. The discharge over a rectangular weir, considering the velocity of approach, is (whereH1 = H + Ha = Total height of water above the weir, H = Height of water over the crest of the weir, and Ha = Height of water due to velocity of approach)
A. (2/3) Cd × L.?2g [H1 - Ha]
B. (2/3) Cd × L. ?2g [H1 ^3/2 - Ha ^3/2]
C. (2/3) Cd × L.?2g [H1 ² - Ha ²]
D. (2/3) Cd × L. ?2g [H1 ^5/2 - Ha ^5/2]
Answer : B

31. A flow whose streamline is represented by a straight line, is called __________ dimensional flow.
A. One
B. Two
C. Three
D. Four
Answer : A

32. Differential manometer is used to measure
A. Pressure in pipes, channels etc.
B. Atmospheric pressure
C. Very low pressure
D. Difference of pressure between two points
Answer : D

33. A glass tube of smaller diameter is used while performing an experiment for the capillary rise of water because
A. It is easier to see through the glass tube
B. Glass tube is cheaper than a metallic tube
C. It is not possible to conduct this experiment with any other tube
D. All of the above
Answer : A

34. The rise or depression of liquid in a tube due to surface tension will increase in size of tube will
A. Increase
B. Remain unaffected
C. May increase or decrease depending on the characteristics of liquid
D. Decrease
Answer : D

35. Pressure of the order of 10 torr can be measured by
A. Bourdon tube
B. Pirani Gauge
C. Micro-manometer
D. Lonisation gauge
Answer : D

36. When the water level on the downstream side of a weir is above the top surface of a weir, the weir is known as
A. Narrow-crested weir
B. Broad-crested weir
C. Ogee weir
D. Submerged weir
Answer : D

37. An open tank containing liquid is moving with an acceleration on an inclined plane. The inclination of the free surface of the liquid will be __________ to the acceleration of the tank.
A. Equal to
B. Directly proportional
C. Inversely proportional
D. None of these
Answer : B

38. Specific weight of sea water is more that of pure water because it contains
A. Dissolved air
B. Dissolved salt
C. Suspended matter
D. All of the above
Answer : D

39. When an internal mouthpiece is running free, the discharge through the mouthpiece is: (where a = Area of mouthpiece, and H = Height of liquid above the mouthpiece)
A. 0.5 a. ?2gH
B. 0.707 a. ?2gH
C. 0.855 a. ?2gH
D. a. ?2gH
Answer : A

40. The pressure in the air space above an oil (sp. gr. 0.8) surface in a tank is 0.1 kg/cm. The pressure at 2.5 m below the oil surface will be
A. 2 metres of water column
B. 3 metres of water column
C. 3.5 metres of water column
D. 4 m of water column
Answer : B

41. The line of action of the buoyant force acts through the
A. Centroid of the volume of fluid vertically above the body
B. Centre of the volume of floating body
C. Center of gravity of any submerged body
D. Centroid of the displaced volume of fluid
Answer : D

42. Fluid is a substance that
A. Cannot be subjected to shear forces
B. Always expands until it fills any container
C. Has the same shear stress at a point regardless of its motion
D. Cannot remain at rest under action of any shear force
Answer : D

43. A piece of wood having weight 5 kg floats in water with 60% of its volume under the liquid. The specific gravity of wood is
A. 0.83
B. 0.6
C. 0.4
D. 0.3
Answer : B

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

45. A vertical wall is subjected to a pressure due to one kind of liquid, on one of its sides. The total pressure on the wall per unit length is (where w = Specific weight of liquid, and H = Height of liquid)
A. wH
B. wH/2
C. wH²/2
D. wH²/3
Answer : C

46. 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

47. Center of buoyancy is the
A. Centroid of the displaced volume of fluid
B. Center of pressure of displaced volume
C. Does not exist
D. None of the above
Answer : A

48. A jet of water discharging from a 40 mm diameter orifice has a diameter of 32 mm at its vena contracta. The coefficient of contraction is
A. 0.46
B. 0.64
C. 0.78
D. 0.87
Answer : B

49. A manometer is used to measure
A. Low pressure
B. Moderate pressure
C. High pressure
D. Atmospheric pressure
Answer : C

50. The flow in which the particles of a fluid attain such velocities that varies from point to point in magnitude and direction as well as from instant to instant, is known as
A. One dimensional flow
B. Uniform flow
C. Steady flow
D. Turbulent flow
Answer : D