1000+ Fluid Mechanics Multiple Choice Question Answer [Solved]

1. The volumetric change of the fluid caused by a resistance is known as
A. Volumetric strain
B. Volumetric index
C. Compressibility
D. Adhesion
Answer : C

2. 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
Answer : C

3. 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

4. The mercury does not wet the glass. This is due to the property of the liquid known as
A. Cohesion
B. Adhesion
C. Viscosity
D. Surface tension
Answer : D

5. The total pressure on the top of a closed cylindrical vessel of radius (r) completely filled up with liquid of specific weight (w) and rotating at (?) rad/s about its vertical axis, is
A. ? w ?² r²/4g
B. ? w ?² r³/4g
C. ? w ?² r?/4g
D. ? w ?² r²/2g
Answer : C

6. 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

7. 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
Answer : D

8. A hydraulic press has a ram of 15 cm diameter and plunger of 1.5 cm. It is required to lift a weight of 1 tonne. The force required on plunger is equal to
A. 10 kg
B. 100 kg
C. 1000 kg
D. 1 kg
Answer : A

9. A fluid is said to be ideal, if it is
A. Incompressible
B. Viscous and incompressible
C. Inviscous and compressible
D. Inviscous and incompressible
Answer : D

10. 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

11. 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

12. 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

13. 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

14. The specific gravity of an oil whose specific weight is 7.85 kN/m3, is
A. 0.8
B. 1
C. 1.2
D. 1.6
Answer : A

15. 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
Answer : C

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

17. 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

18. Reynolds 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 : B

19. The coefficient of viscosity may be determined by
A. Capillary tube method
B. Orifice type viscometer
C. Rotating cylinder method
D. All of these
Answer : D

20. Pitot tube is used for measurement of
A. Pressure
B. Flow
C. Velocity
D. Discharge
Answer : C

21. Buoyant force is
A. Resultant force acting on a floating body
B. Equal to the volume of liquid displaced
C. Force necessary to keep a body in equilibrium
D. The resultant force on a body due to the fluid surrounding it
Answer : D

22. The flow in which conditions do not change with time at any point, is known as
A. One dimensional flow
B. Uniform flow
C. Steady flow
D. Turbulent flow
Answer : C

23. The siphon will work satisfactorily, if the minimum pressure in the pipe is __________ vapour pressure of liquid.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : C

24. When a liquid is flowing through a pipe, the velocity of the liquid is
A. Maximum at the centre and minimum near the walls
B. Minimum at the centre and maximum near the walls
C. Zero at the centre and maximum near the walls
D. Maximum at the centre and zero near the walls
Answer : A

25. The horizontal component of buoyant force is
A. Negligible
B. Same as buoyant force
C. Zero
D. None of the above
Answer : C

26. 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

27. Practical fluids
A. Are viscous
B. Possess surface tension
C. Are compressible
D. Possess all the above properties
Answer : D

28. 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
Answer : D

29. The Cipoletti weir is a __________ weir.
A. Rectangular
B. Triangular
C. Trapezoidal
D. Circular
Answer : C

30. In a short cylindrical external mouthpiece, the vena contracta occurs at a distance __________ the diameter of the orifice from the outlet of orifice.
A. Equal to
B. One-fourth
C. One-third
D. One-half
Answer : B

31. The pressure at a point 4 m below the free surface of water is
A. 19.24 kPa
B. 29.24 kPa
C. 39.24 kPa
D. 49.24 kPa
Answer : C

32. The Euler's equation for the motion of liquids is based upon the assumption that
A. The fluid is non - viscous, homogeneous and incompressible
B. The velocity of flow is uniform over the section
C. The flow is continuous, steady and along the stream line
D. All of the above
Answer : D

33. 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

34. The discharge over a rectangular notch is
A. Inversely proportional to H^3/2
B. Directly proportional to H^3/2
C. Inversely proportional to H^5/2
D. Directly proportional to H^5/2
Answer : B

35. A ship whose hull length is 100 m is to travel at 10 m/sec. For dynamic similarity, at what velocity should a 1:25 model be towed through water?
A. 10 m/sec
B. 25 m/sec
C. 2 m/sec
D. 50 m/sec
Answer : C

36. 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
Answer : B

37. Reynold's number is the ratio of the inertia force to the
A. Surface tension force
B. Viscous force
C. Gravity force
D. Elastic force
Answer : B

38. The loss of pressure head in case of laminar flow is proportional to
A. Velocity
B. (Velocity)²
C. (Velocity)³
D. (Velocity)⁴
Answer : A

39. The bulk modulus of elasticity
A. Has the dimensions of 1/pressure
B. Increases with pressure
C. Is large when fluid is more compressible
D. Is independent of pressure and viscosity
Answer : B

40. To avoid vaporisation in the pipe line, the pipe line over the ridge is laid such that it is not more than
A. 2.4 m above the hydraulic gradient
B. 6.4 m above the hydraulic gradient
C. 10.0 m above the hydraulic gradient
D. 5.0 above the hydraulic gradient
Answer : B

41. Which of the following statement is wrong?
A. A flow whose streamline is represented by a curve is called two dimensional flow.
B. The total energy of a liquid particle is the sum of potential energy, kinetic energy and pressure energy.
C. The length of divergent portion in a Venturimeter is equal to the convergent portion.
D. A pitot tube is used to measure the velocity of flow at the required point in a pipe.
Answer : C

42. 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

43. 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

44. Viscous force is the __________ of shear stress due to viscosity and cross-section area of flow.
A. Sum
B. Different
C. Product
D. Ratio
Answer : C

45. 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

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
Answer : C

47. Which of the following instrument can be used for measuring speed of a submarine moving in deep sea?
A. Venturimeter
B. Orifice plate
C. Hot wire anemometer
D. Pitot tube
Answer : D

48. The discharge through a channel of circular section will be maximum when the depth of water is __________ the diameter of the circular channel.
A. 0.34 times
B. 0.67 times
C. 0.81 times
D. 0.95 times
Answer : D

49. 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

50. The most efficient section of a channel is
A. Triangular
B. Rectangular
C. Square
D. Trapezoidal
Answer : D