Fluid Mechanics 1000+ MCQ with answer for FCI Recruitment

1. The flow in a pipe is turbulent when Reynold number is
A. Less than 2000
B. Between 2000 and 2800
C. More than 2800
D. None of these
Answer : C

2. The increase of temperature results in
A. Increase in viscosity of gas
B. Increase in viscosity of liquid
C. Decrease in viscosity of gas
D. Decrease in viscosity of liquid
Answer : D

3. The sheet of water flowing over a notch or a weir is known as
A. Sill or crest
B. Nappe or vein
C. Orifice
D. None of these
Answer : B

4. A water tank contains 1.3 m deep water. The pressure exerted by the water per metre length of the tank is
A. 2.89 kN
B. 8.29 kN
C. 9.28 kN
D. 28.9 kN
Answer : B

5. In an immersed body, centre of pressure is
A. At the centre of gravity
B. Above the centre of gravity
C. Below be centre of gravity
D. Could be above or below e.g. depending on density of body and liquid
Answer : C

6. Piezometer is used to measure
A. Pressure in pipe, channels etc.
B. Atmospheric pressure
C. Very low pressures
D. Difference of pressure between two points
Answer : C

7. The mass 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 : B

8. 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

9. According to Newton's law of viscosity, the shear stress on a layer of a fluid is __________ to the rate of shear strain.
A. Equal to
B. Directly proportional
C. Inversely proportional
D. None of these
Answer : B

10. The height of a water column equivalent to a pressure of 0.15 MPa is
A. 15.3 m
B. 25.3 m
C. 35.3 m
D. 45.3 m
Answer : A

11. The Metacentric heights of two floating bodies A and B are 1 m and 1.5 m respectively. Select the correct statement.
A. The bodies A and B have equal stability
B. The body A is more stable than body B
C. The body B is more stable than body A
D. The bodies A and B are unstable
Answer : C

12. 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

13. Euler's number is the ratio of __________ force to pressure force.
A. Inertia
B. Gravity
C. Viscous
D. None of these
Answer : A

14. According to Darcy's formula, the loss of head due to friction in the pipe is (where f = Darcy's coefficient, l = Length of pipe, v = Velocity of liquid in pipe, and d = Diameter of pipe)
A. flv²/2gd
B. flv²/gd
C. 3flv²/2gd
D. 4flv²/2gd
Answer : D

15. The vapour pressure over the concave surface is
A. Less man the vapour pressure over the plane surface
B. Equal to the vapour pressure over the plane surface
C. Greater than the vapour pressure over the plane surface
D. Zero
Answer : A

16. The pressure of a liquid measured with the help of a Piezometer tube is
A. Vacuum pressure
B. Gauge pressure
C. Absolute pressure
D. Atmospheric pressure
Answer : B

17. Froude's number is the ratio of inertia force to
A. Pressure force
B. Elastic force
C. Gravity force
D. Surface tension force
Answer : C

18. In an isothermal atmosphere, the pressure
A. Decreases linearly with elevation
B. Remain constant
C. Varies in the same way as the density
D. Increases exponentially with elevation
Answer : C

19. A perfect gas
A. Has constant viscosity
B. Has zero viscosity
C. Is in compressible
D. None of the above
Answer : D

20. 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

21. Froude number is significant in
A. Supersonics, as with projectile and jet propulsion
B. Full immersion or completely enclosed flow, as with pipes, aircraft wings, nozzles etc.
C. Simultaneous motion through two fluids where there is a surface of discontinuity, gravity forces, and wave making effect as with ship's hulls
D. All of the above
Answer : C

22. The total pressure on an immersed surface inclined at an angle ? with the liquid surface is
A. wA
B. wx
C. wAx
D. wAx/sin?
Answer : C

23. The pressure of fluid due to hammer blow is
A. Directly proportional to density of fluid
B. Inversely proportional to density of fluid
C. Directly proportional to (density)^1/2 of fluid
D. Inversely proportional to (density)^1/2 of fluid
Answer : C

24. 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

25. When a cylindrical vessel containing liquid is resolved, the surface of the liquid takes the shape of
A. A triangle
B. A paraboloid
C. An ellipse
D. None of these
Answer : B

26. 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

27. The dynamic viscosity of gases __________ with rise in temperature.
A. Remain unaffected
B. Increases
C. Decreases
D. None of these
Answer : B

28. Coefficient of resistance is the ratio of
A. Actual velocity of jet at vena-contracta to the theoretical velocity
B. Area of jet at vena-contracta to the area of orifice
C. Loss of head in the orifice to the head of water available at the exit of the orifice
D. Actual discharge through an orifice to the theoretical discharge
Answer : C

29. The magnitude of water hammer depends upon the
A. Elastic properties of the pipe material
B. Elastic properties of the liquid flowing through the pipe
C. Speed at which the valve is closed
D. All of the above
Answer : D

30. For a floating body to be in equilibrium
A. Meta centre should be above e.g.
B. Centre of buoyancy and e.g. must lie on same vertical plane
C. A righting couple should be formed
D. All of the above
Answer : D

31. The error in discharge (dQ/Q) to the error in measurement of head (dH/H) over a rectangular notch is given by
A. dQ/Q = (1/2) × (dH/H)
B. dQ/Q = (3/4) × (dH/H)
C. dQ/Q = (dH/H)
D. dQ/Q = (3/2) × (dH/H)
Answer : D

32. 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

33. In case of flow through parallel pipes,
A. The head loss for all the pipes is same
B. The total discharge is equal to the sum of discharges in the various pipes
C. The total head loss is the sum of head losses in the various pipes
D. Both (A) and (B)
Answer : D

34. A venturi-flume is used to measure
A. Pressure of liquid
B. Discharge of liquid
C. Pressure difference between two points in a channel
D. Pressure difference between two points in a pipe
Answer : B

35. The units of kinematic viscosity are
A. Metres² per sec
B. kg sec/metre
C. Newton-sec per metre
D. Newton-sec per metre
Answer : A

36. 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

37. 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

38. An open vessel of water is accelerated up an inclined plane. The free water surface will
A. Be horizontal
B. Make an angle in direction of inclination of inclined plane
C. Make an angle in opposite direction to inclination of inclined plane
D. Any one of above is possible
Answer : C

39. Dynamic viscosity of most of the liquids with rise in temperature
A. Increases
B. Decreases
C. Remain unaffected
D. Unpredictable
Answer : B

40. 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

41. Hydrometer is used to determine
A. Specific gravity of liquids
B. Specific gravity of solids
C. Specific gravity of gases
D. Relative humidity
Answer : A

42. 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

43. 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

44. The total energy line lies over the hydraulic gradient line by an amount equal to the
A. Pressure head
B. Velocity head
C. Pressure head + velocity head
D. Pressure head - velocity head
Answer : B

45. A nozzle is generally made of
A. Cylindrical shape
B. Convergent shape
C. Divergent shape
D. Convergent-divergent shape
Answer : B

46. 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

47. The discharge in an open channel corresponding to critical depth is
A. Zero
B. Minimum
C. Maximum
D. None of these
Answer : C

48. In order to measure the flow with a Venturimeter, it is installed in
A. Horizontal line
B. Inclined line with flow upwards
C. Inclined line with flow downwards
D. Any direction and in any location
Answer : D

49. Free surface of a liquid tends to contract to the smallest possible area due to force of
A. Surface tension
B. Viscosity
C. Friction
D. Cohesion
Answer : A

50. The pressure less than atmospheric pressure is known as
A. Suction pressure
B. Vacuum pressure
C. Negative gauge pressure
D. All of these
Answer : D