Fluid Mechanics MCQ Solved Paper for RBI Assistant

1. 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

2. The discharge through a convergent mouthpiece is __________ the discharge through an internal mouthpiece of the same diameter and head of water.
A. Equal to
B. One-half
C. Three fourth
D. Double
Answer : D

3. In order to increase sensitivity of U-tube manometer, one leg is usually inclined by angle ?. Sensitivity of inclined tube to sensitivity of Utube is equal to
A. Sin?
B. 1/Sin?
C. Cos?
D. 1/Cos?
Answer : B

4. Which of the following manometer has highest sensitivity?
A. U-tube with water
B. Inclined U-tube
C. U-tube with mercury
D. Micro-manometer with water
Answer : D

5. When the coefficient of discharge (Cd) is 0.623, then the general equation for discharge over a rectangular weir is
A. 1.84 (L - 0.1nH)H^3/2
B. 1.84 (L - nH)H²
C. 1.84 (L - 0.1nH)H^5/2
D. 1.84 (L - nH)H³
Answer : A

6. 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

7. 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

8. When a body floating in a liquid, is displaced slightly, it oscillates about
A. C.G. of body
B. Center of pressure
C. Center of buoyancy
D. Metacentre
Answer : D

9. 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

10. 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

11. Resultant pressure of the liquid in the case of an immersed body acts through
A. Centre of gravity
B. Centre of pressure
C. Metacentre
D. Centre of buoyancy
Answer : B

12. A hemispherical tank of radius (R) has an orifice of cross-sectional area (a) at its bottom and is full of liquid. The time required to empty the tank completely is
A. 14? R^1/2/15C_d × a ?(2g)
B. 14? R^3/2/15C_d × a ?(2g)
C. 14? R^5/2/15C_d × a ?(2g)
D. 14? R^7/2/15C_d × a ?(2g)
Answer : C

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

14. 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

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

16. A flow in which each liquid particle has a definite path, and the paths of individual particles do not cross each other, is called
A. Steady flow
B. Uniform flow
C. Streamline flow
D. Turbulent flow
Answer : C

17. 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

18. According to the principle of buoyancy a body totally or partially immersed in a fluid will be lifted up by a force equal to
A. The weight of the body
B. More than the weight of the body
C. Less than the weight of the body
D. Weight of the fluid displaced by the body
Answer : D

19. The length of the divergent cone in a Venturimeter is __________ that of the convergent cone.
A. Equal to
B. Double
C. Three to four times
D. Five to six times
Answer : C

20. A pipe of length more than double the diameter of orifice fitted externally or internally to the orifice is called a
A. Notch
B. Weir
C. Mouthpiece
D. Nozzle
Answer : C

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

22. 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

23. 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

24. If no resistance is encountered by displacement, such a substance is known as
A. Fluid
B. Water
C. Gas
D. Ideal fluid
Answer : D

25. The pressure measured with the help of a pressure gauge is called
A. Atmospheric pressure
B. Gauge pressure
C. Absolute pressure
D. Mean pressure
Answer : B

26. Capillary action is due to the
A. Surface tension
B. Cohesion of the liquid
C. Adhesion of the liquid molecules and the molecules on the surface of a solid
D. All of the above
Answer : D

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

28. A large Reynold number is indication of
A. Smooth and streamline flow
B. Laminar flow
C. Steady flow
D. Highly turbulent flow
Answer : D

29. 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

30. 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

31. 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

32. When the Mach number is more than 6, the flow is called
A. Sub-sonic flow
B. Sonic flow
C. Super-sonic flow
D. Hyper-sonic flow
Answer : D

33. In order to avoid tendency of separation at throat in a Venturimeter, the ratio of the diameter at throat to the diameter of pipe should be
A. 1/16 to 1/8
B. 1/8 to 1/4
C. 1/4 to 1/3
D. 1/3 to 1/2
Answer : D

34. 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

35. Gradually varied flow is
A. Steady uniform
B. Non-steady non-uniform
C. Non-steady uniform
D. Steady non-uniform
Answer : D

36. The coefficient of discharge for an external mouthpiece depends upon
A. Velocity of liquid
B. Pressure of liquid
C. Area of mouthpiece
D. Length of mouthpiece
Answer : D

37. An ideal flow of any fluid must satisfy
A. Pascal law
B. Newton's law of viscosity
C. Boundary layer theory
D. Continuity equation
Answer : D

38. The stability of a dam is checked for
A. Tension at the base
B. Overturning of the wall or dam
C. Sliding of the wall or dam
D. All of these
Answer : D

39. The unit of dynamic viscosity in S.I. units is
A. N-m/s²
B. N-s/m²
C. Poise
D. Stoke
Answer : B

40. The diameter of the nozzle (d) for maximum transmission of power is given by (where D = Diameter of pipe, f = Darcys coefficient of friction for pipe, and l = Length of pipe)
A. d = (D?/8fl)^1/2
B. d = (D?/8fl)^1/3
C. d = (D?/8fl)^1/4
D. d = (D?/8fl)^1/5
Answer : C

41. The total energy line lies over the centre line of the pipe by an amount equal to
A. Pressure head
B. Velocity head
C. Pressure head + velocity head
D. Pressure head - velocity head
Answer : C

42. An error of 1% in measuring head over the crest 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

43. When a body is placed over a liquid, it will sink down if
A. Gravitational force is equal to the up-thrust of the liquid
B. Gravitational force is less than the up-thrust of the liquid
C. Gravitational force is more than the up-thrust of the liquid
D. None of the above
Answer : C

44. Property of a fluid by which molecules of different kinds of fluids are attracted to each other is called
A. Adhesion
B. Cohesion
C. Viscosity
D. Compressibility
Answer : A

45. A glass tube of small diameter (d) is dipped in fluid. The height of rise or fall in the tube given by (where w = Speciic weight of liquid, ? = Angle of contact of the liquid surface, and ? = Surface tension)
A. 4wd/? cos?
B. ? cos?/4wd
C. 4? cos?/wd
D. wd/4? cos?
Answer : C

46. The total pressure on a horizontally immersed surface is (where w = Specific weight of the liquid, A = Area of the immersed surface, and x = Depth of the centre of gravity of the immersed surface from the liquid surface)
A. wA
B. wx
C. wAx
D. wA/x
Answer : C

47. 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

48. 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

49. The process of diffusion of one liquid into the other through a semi permeable membrane is called
A. Viscosity
B. Osmosis
C. Surface tension
D. Cohesion
Answer : B

50. The divergent portion of a Venturimeter is made longer than convergent portion in order to
A. Avoid the tendency of breaking away the stream of liquid
B. To minimise frictional losses
C. Both (A) and (B)
D. None of these
Answer : C