### Multiple Choice Questions (MCQs) and Answers on Fluid Mechanics

01. 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

02. The property by virtue of which a liquid opposes relative motion between its different layers is called

(A) Surface tension
(B) Coefficient of viscosity
(C) Viscosity
(D) Osmosis

03. A weir is said to be narrow-crested weir, if the width of the crest of the weir is __________ half the height of water above the weir crest.

(A) Equal to
(B) Less than
(C) More than
(D) None of these

04. Euler’s dimensionless number relates the following

(A) Inertial force and gravity
(B) Viscous force and inertial force
(C) Viscous force and buoyancy force
(D) Pressure force and inertial force

05. 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

06. The pressure of the liquid flowing through the divergent portion of a Venturimeter

(A) Remains constant
(B) Increases
(C) Decreases
(D) Depends upon mass of liquid

07. 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

08. 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

09. A vertically immersed surface is shown in the below figure. The distance of its centre of pressure from the water surface is (A) (bd²/12) + x̅
(B) (d²/12 x̅) + x̅
(C) b²/12 + x̅
(D) d²/12 + x̅

10. The torque required to overcome viscous resistance of a collar bearing is (where R1 andR2 = External and internal radius of collar)

(A) (μπ²N/60t) × (R₁ – R₂)
(B) (μπ²N/60t) × (R₁² – R₂²)
(C) (μπ²N/60t) × (R₁³ – R₂³)
(D) (μπ²N/60t) × (R₁⁴ – R₂⁴)

(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

12. A flow is called super-sonic if the

(A) Velocity of flow is very high
(B) Discharge is difficult to measure
(C) Mach number is between 1 and 6
(D) None of these

13. In a forced vortex, the velocity of flow everywhere within the fluid is

(A) Maximum
(B) Minimum
(C) Zero
(D) Nonzero finite

14. The depth of centre of pressure (h) for a vertically immersed surface from the liquid surface is given by (where IG = Moment of inertia of the immersed surface about horizontal axis through its centre of gravity, A = Area of immersed surface, and x = Depth of centre of gravity of the immersed surface from the liquid surface)

(A) (IG/Ax̅) – x̅
(B) (IG/x̅) – Ax̅
(C) (Ax̅/IG) + x̅
(D) (IG/Ax̅) + x̅

15. Mach number is significant in

(A) Supersonics, as with projectiles 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 force, and wave making effects, as with ship’s hulls
(D) All of the above

16. A fluid which obeys the Newton’s law of viscosity is termed as

(A) Real fluid
(B) Ideal fluid
(C) Newtonian fluid
(D) Non-Newtonian fluid

17. In order that flow takes place between two points in a pipeline, the differential pressure between these points must be more than

(A) Frictional force
(B) Viscosity
(C) Surface friction
(D) All of the above

18. The error in discharge (dQ/Q) to the error in measurement of head (dH/H) over a triangular notch is given by

(A) dQ/Q = 3/2 × (dH/H)
(B) dQ/Q = 2 × (dH/H)
(C) dQ/Q = 5/2 × (dH/H)
(D) dQ/Q = 3 × (dH/H)

19. For similarity, in addition to models being geometrically similar to prototype, the following in both cases should also be equal

(A) Ratio of inertial force to force due to viscosity
(B) Ratio of inertial force to force due to gravitation
(C) Ratio of inertial force to force due to surface tension
(D) All the four ratios of inertial force to force due to viscosity, gravitation, surface tension, and elasticity

20. The value of coefficient of velocity for a sharp edged orifice __________ with the head of water.

(A) Decreases
(B) Increases
(C) Remain same
(D) None of these

21. If cohesion between molecules of a fluid is greater than adhesion between fluid and glass, then the free level of fluid in a dipped glass tube will be

(A) Higher than the surface of liquid
(B) The same as the surface of liquid
(C) Lower than the surface of liquid
(D) Unpredictable

22. 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

23. A one dimensional flow is one which

(A) Is uniform flow
(C) Takes place in straight lines
(D) Involves zero transverse component of flow

24. According to Manning’s formula, the discharge through an open channel is (where M = Manning’s constant)

(A) A × M × m1/2 × i2/3
(B) A × M × m2/3 × i1/2
(C) A1/2 × M2/3 × m × i
(D) A2/3 × M1/3 × m × i

25. Dimensions of surface tension are (A) ML°T⁻² (B) ML°T (C) ML r² (D) ML²T² Answer: Option A 26. An opening in the side of a tank or vessel such that the liquid surface with the tank is below the top edge of the opening, is called

(A) Weir
(B) Notch
(C) Orifice
(D) None of these

27. The property of fluid by virtue of which it offers resistance to shear is called

(A) Surface tension
(C) Cohesion
(D) Viscosity

28. Coefficient of velocity is defined as 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) Actual discharge through an orifice to the theoretical discharge
(D) None of the above

29. A liquid compressed in cylinder has a volume of 0.04 m3 at 50 kg/cm² and a volume of 0.039 m3 at 150 kg/cm². The bulk modulus of elasticity of liquid is

(A) 400 kg/cm²
(B) 4000 kg/cm²
(C) 40 × 10⁵ kg/cm²
(D) 40 × 10⁶ kg/cm²

30. 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

31. A fluid in equilibrium can’t sustain

(A) Tensile stress
(B) Compressive stress
(C) Shear stress
(D) Bending stress

32. When a plate is immersed in a liquid parallel to the flow, it will be subjected to a pressure __________ that if the same plate is immersed perpendicular to the flow.

(A) Less than
(B) More than
(C) Equal to
(D) None of these

33. An object having 10 kg mass weighs 9.81 kg on a spring balance. The value of ‘g’ at this place is

(A) 10 m/sec²
(B) 9.81 m/sec²
(C) 9.75 m/sec²
(D) 9 m/sec

34. 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

35. Liquids

(A) Cannot be compressed
(B) Occupy definite volume
(C) Are not affected by change in pressure and temperature
(D) None of the above

36. 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

37. 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

38. The force exerted by a moving fluid on an immersed body is directly proportional to the rate of change of momentum due to the presence of the body. This statement is called

(A) Newton’s law of motion
(B) Newton’s law of cooling
(C) Newton’s law of viscosity
(D) Newton’s law of resistance

39. The property of a fluid which enables it to resist tensile stress is known as

(A) Compressibility
(B) Surface tension
(C) Cohesion

40. The loss of pressure head in case of laminar flow is proportional to

(A) Velocity
(B) (Velocity)2
(C) (Velocity)3
(D) (Velocity)4

41. The surface tension of mercury at normal temperature compared to that of water is

(A) More
(B) Less
(C) Same
(D) More or less depending on size of glass tube

42. An air vessel is provided at the summit in a siphon to

(A) Avoid interruption in the flow
(B) Increase discharge
(C) Increase velocity
(D) Maintain pressure difference

43. The unit of viscosity is

(A) Metres² per sec
(B) kg-sec/metre
(C) Newton-sec per metre²
(D) Newton-sec per meter

44. Select the correct statement

(A) Weber’s number is the ratio of inertia force to elastic force.
(B) Weber’s number is the ratio of gravity force to surface tension force.
(C) Weber’s number is the ratio of viscous force to pressure force.
(D) Weber’s number is the ratio of inertia force to surface tension force.

45. Choose the wrong statement. Alcohol is used in manometer, because

(A) Its vapour pressure is low
(B) It provides suitable meniscus for the inclined tube
(C) Its density is less
(D) It provides longer length for a given pressure difference

46. When a tank containing liquid moves with an acceleration in the horizontal direction, then the free surface of the liquid

(A) Remains horizontal
(B) Becomes curved
(C) Falls on the front end
(D) Falls on the back end

47. A pressure of 25 m of head of water is equal to

(A) 25 kN/ m²
(B) 245 kN/ m²
(C) 2500 kN/m²
(D) 2.5 kN/ m²

48. The hammer blow in pipes occurs when

(A) There is excessive leakage in the pipe
(B) The pipe bursts under high pressure of fluid
(C) The flow of fluid through the pipe is suddenly brought to rest by closing of the valve
(D) The flow of fluid through the pipe is gradually brought to rest by closing of the valve

49. The resultant upward pressure of the fluid on an immersed body is called

(A) Up-thrust
(B) Buoyancy
(C) Center of pressure
(D) All the above are correct