1000+ Fluid Mechanics MCQ for RBI Grade B officer [Solved]

1. The Francis formula for the discharge over Cipoletti weir is
A. 1.84 LH^1/2
B. 1.84 LH
C. 1.84 LH^3/2
D. 1.84 LH^5/2
Answer : C

2. Normal depth in open channel flow is the depth of flow corresponding to
A. Steady flow
B. Unsteady flow
C. Laminar flow
D. Uniform flow
Answer : D

3. Kinematic viscosity is equal to
A. Dynamic viscosity/density
B. Dynamic viscosity × density
C. Density/dynamic viscosity
D. 1/dynamic viscosity × density
Answer : A

4. Viscosity of water in comparison to mercury is
A. Higher
B. Lower
C. Same
D. Higher/lower depending on temperature
Answer : A

5. 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

6. According to Chezy's formula, the discharge through an open channel is (where A = Area of flow, C = Chezy's constant, m = Hydraulic mean depth, and i = Uniform slope in bed)
A. A × ?(m × i)
B. C × ?(m × i)
C. AC × ?(m × i)
D. mi × ?(A × C)
Answer : C

7. Choose the correct relationship
A. Specific gravity = gravity × density
B. Dynamic viscosity = kinematic viscosity × density
C. Gravity = specific gravity × density
D. Kinematic viscosity = dynamic viscosity × density
Answer : B

8. The stress-strain relation of the Newtonian fluid is
A. Linear
B. Parabolic
C. Hyperbolic
D. Inverse type
Answer : A

9. The flow of water through the hole in the bottom of a wash basin is an example of
A. Steady flow
B. Uniform flow
C. Free vortex
D. Forced vortex
Answer : C

10. A submerged body is said to be in a stable equilibrium, if its centre of gravity __________ the centre of buoyancy.
A. Coincides with
B. Lies below
C. Lies above
D. None of these
Answer : B

11. The flow in which each liquid particle has a definite path and their paths do not cross each other is called
A. One dimensional flow
B. Streamline flow
C. Steady flow
D. Turbulent flow
Answer : B

12. The efficiency of power transmission through pipe is (where H = Total supply head, and hf = Head lost due to friction in the pipe)
A. (H - hf )/H
B. H/(H - hf )
C. (H + hf )/H
D. H/(H + hf )
Answer : A

13. A flow is called hyper-sonic, if the Mach number is
A. Less than unity
B. Unity
C. Between 1 and 6
D. None of these
Answer : D

14. The depth of the centre of pressure on a vertical rectangular gate 8 m wide and 6 m high, when the water surface coincides with the top of the gate, is
A. 2.4 m
B. 3.0 m
C. 4.0 m
D. 5.0 m
Answer : B

15. Surface energy per unit area of a surface is numerically equal to
A. Atmospheric pressure
B. Surface tension
C. Force of adhesion
D. Force of cohesion
Answer : B

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

17. 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

18. The kinematic viscosity is the
A. Ratio of absolute viscosity to the density of the liquid
B. Ratio of density of the liquid to the absolute viscosity
C. Product of absolute viscosity and density of the liquid
D. Product of absolute viscosity and mass of the liquid
Answer : A

19. 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

20. A thick liquid like syrup has a __________ viscosity than a light liquid like water.
A. Lesser
B. Greater
C. Same
D. None of these
Answer : B

21. The viscosity of a liquid __________ its rate of flow through a hole in a vessel.
A. Effects
B. Does not effect
C. Both A and B
D. None of these
Answer : A

22. 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

23. Select the correct statement
A. Local atmospheric pressure depends upon elevation of locality only
B. Standard atmospheric pressure is the mean local atmospheric pressure a* sea level
C. Local atmospheric pressure is always below standard atmospheric pressure
D. A barometer reads the difference between local and standard atmospheric pressure
Answer : B

24. 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

25. The discharge through a channel of rectangular section will be maximum, if
A. Its depth is twice the breadth
B. Its breadth is twice the depth
C. Its depth is thrice the breadth
D. Its breadth is thrice the depth
Answer : B

26. 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

27. 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

28. The flow in a pipe is neither laminar nor turbulent when Reynold number is
A. Less than 2000
B. Between 2000 and 2800
C. More than 2800
D. None of these
Answer : B

29. In an external mouthpiece, the absolute pressure head at vena contracta is __________ the atmospheric pressure head by an amount equal to 0.89 times the height of the liquid, above the vena contracta.
A. Less than
B. More than
C. Equal to
D. None of these
Answer : A

30. Euler's equation in the differential form for the motion of liquids is given by
A. dp/? + g.dz + v.dv = 0
B. dp/? - g.dz + v.dv = 0
C. ?.dp + g.dz + v.dv = 0
D. ?.dp - g.dz + v.dv = 0
Answer : A

31. A balloon lifting in air follows the following principle
A. Law of gravitation
B. Archimedes principle
C. Principle of buoyancy
D. All of the above
Answer : D

32. The pressure of air __________ with the increase of height from the surface of the earth.
A. Does not change
B. Decreases
C. Increases
D. None of these
Answer : B

33. The length AB of a pipe ABC in which the liquid is flowing has diameter (d1) and is suddenly enlarged to diameter (d2) at B which is constant for the length BC. The loss of head due to sudden enlargement is
A. (v? - v?)²/g
B. (v?² - v?²)/g
C. (v? - v?)²/2g
D. (v?² - v?²)/2g
Answer : C

34. When the flow in an open channel is gradually varied, the flow is said to be
A. Steady uniform flow
B. Steady non-uniform flow
C. Unsteady uniform flow
D. Unsteady non-uniform flow
Answer : B

35. For a body floating in a liquid the normal pressure exerted by the liquid acts at
A. Bottom surface of the body
B. C.G. of the body
C. Metacentre
D. All points on the surface of the body
Answer : D

36. A flow in which the quantity of liquid flowing per second is not constant, is called
A. Streamline flow
B. Turbulent flow
C. Steady flow
D. Unsteady flow
Answer : D

37. Whenever a plate is held immersed at some angle with the direction of flow of the liquid, it is subjected to some pressure. The component of this pressure, in the direction of flow of the liquid, is known as
A. Lift
B. Drag
C. Stagnation pressure
D. Bulk modulus
Answer : B

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

39. In a forced vortex, the velocity of flow everywhere within the fluid is
A. Maximum
B. Minimum
C. Zero
D. Nonzero finite
Answer : D

40. 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

41. The conditions for the stable equilibrium of a floating body are
A. The metacentre should lie above the center of gravity
B. The center of buoyancy and the center of gravity must lie on the same vertical line
C. A righting couple should be formed
D. All the above are correct
Answer : D

42. Which of the following is dimensionless?
A. Specific weight
B. Specific volume
C. Specific speed
D. Specific gravity
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. 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

45. With an increase in size of tube, the rise or depression of liquid in the tube due to surface tension will
A. Decrease
B. Increase
C. Remain unchanged
D. Depend upon the characteristics of liquid
Answer : A

46. A metal with specific gravity of a floating in a fluid of same specific gravity a will
A. Sink to bottom
B. Float over fluid
C. Partly immersed
D. Be fully immersed with top surface at fluid surface
Answer : D

47. The total pressure on the top of a closed cylindrical vessel completely filled up with a liquid is
A. Directly proportional to (radius)²
B. Inversely proportional to (radius)²
C. Directly proportional to (radius)⁴
D. Inversely proportional to (radius)⁴
Answer : C

48. 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

49. An open tank containing liquid is made to move from rest with a uniform acceleration. The angle 0 which the free surface of liquid makes with the horizontal is such that (where a = Horizontal acceleration of the tank, and g = Acceleration due to gravity)
A. tan? = a/g
B. tan? = 2 a/g
C. tan? = a/2g
D. tan? = a2/2g
Answer : A

50. If 850 kg liquid occupies volume of one cubic meter, men 0.85 represents its
A. Specific weight
B. Specific mass
C. Specific gravity
D. Specific density
Answer : C