Fluid Mechanics 1000+ MCQ with answer for UPSC IES

1. 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
Answer : A

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

3. 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

4. A vertical wall is subjected to a pressure due to one kind of liquid, on one of its sides. The total pressure on the wall acts at a distance __________ from the liquid surface.
A. H/3
B. H/2
C. 2H/3
D. 3H/4
Answer : C

5. The velocity corresponding to Reynold number of 2800, is called
A. Sub-sonic velocity
B. Super-sonic velocity
C. Lower critical velocity
D. Higher critical velocity
Answer : D

6. A flow through an expanding tube at constant rate is called
A. Steady uniform flow
B. Steady non-uniform flow
C. Unsteady uniform flow
D. Unsteady non-uniform flow
Answer : B

7. Falling drops of water become spheres due to the property of
A. Adhesion
B. Cohesion
C. Surface tension
D. Viscosity
Answer : C

8. The discharge over a rectangular notch is (where b = Width of notch, and H = Height of liquid, above the sill of the notch)
A. (2/3) C_d × b × ?(2gH)
B. (2/3) C_d × b × ?(2g) × H
C. (2/3) C_d × b × ?(2g) × H^3/2
D. (2/3) C_d × b × ?(2g) × H²
Answer : C

9. 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
Answer : D

10. A compound pipe is required to be replaced by a new pipe. The two pipes are said to be equivalent, if
A. Length of both the pipes is same
B. Diameter of both the pipes is same
C. Loss of head and discharge of both the pipes is same
D. Loss of head and velocity of flow in both the pipes is same
Answer : C

11. Flow occurring in a pipeline when a valve is being opened is
A. Steady
B. Unsteady
C. Laminar
D. Vortex
Answer : B

12. The liquid used in manometers should have
A. Low density
B. High density
C. Low surface tension
D. High surface tension
Answer : D

13. A structure, whose width is __________ the width of the channel, is called a flumed structure.
A. Less than
B. More than
C. Equal
D. None of these
Answer : A

14. 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
Answer : A

15. 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
Answer : B

16. 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

17. The body will sink down if the force of buoyancy is __________ the weight of the liquid displaced.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : B

18. 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

19. 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

20. 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

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

22. The tangential velocity of the water element having a free vortex is
A. Directly proportional to its distance from the centre
B. Inversely proportional to its distance from the centre
C. Directly proportional to its (distance)² from the centre
D. Inversely proportional to its (distance)² from the centre
Answer : B

23. 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

24. The property of a fluid which enables it to resist tensile stress is known as
A. Compressibility
B. Surface tension
C. Cohesion
D. Adhesion
Answer : C

25. 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

26. 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

27. The resultant of all normal pressures acts
A. At C.G. of body
B. At center of pressure
C. Vertically upwards
D. At metacentre
Answer : C

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

29. A tank of uniform cross-sectional area (A) containing liquid upto height (H1) has an orifice of cross-sectional area (a) at its bottom. The time required to empty the tank completely will be
A. (2A?H?)/(C_d × a?2g)
B. (2AH?)/(C_d × a?2g)
C. (2AH?^3/2)/(C_d × a?2g)
D. (2AH?²)/(C_d × a?2g)
Answer : A

30. For hypersonic flow, the Mach number is
A. Unity
B. Greater than unity
C. Greater than 2
D. Greater than 4
Answer : D

31. When the water level on the downstream side of a weir is above the top surface of a weir, the weir is known as
A. Narrow-crested weir
B. Broad-crested weir
C. Ogee weir
D. Submerged weir
Answer : D

32. A flow in which the volume of a fluid and its density does not change during the flow is called _________ flow.
A. Incompressible
B. Compressible
C. Viscous
D. None of these
Answer : A

33. 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

34. 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

35. 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

36. The viscosity of water at 20°C is
A. One stoke
B. One centistoke
C. One poise
D. One centipoise
Answer : D

37. The loss of head due to friction in a pipe of uniform diameter in which a viscous flow is taking place, is (where RN = Reynold number)
A. 1/R_N
B. 4/R_N
C. 16/R_N
D. 64/R_N
Answer : C

38. Choose the wrong statement
A. Viscosity of a fluid is that property which determines the amount of its resistance to a shearing force
B. Viscosity is due primarily to interaction between fluid molecules
C. Viscosity of liquids decreases with increase in temperature
D. Viscosity of liquids is appreciably affected by change in pressure
Answer : D

39. The buoyancy depends on
A. Mass of liquid displaced
B. Viscosity of the liquid
C. Pressure of the liquid displaced
D. Depth of immersion
Answer : A

40. The ratio of the inertia force to the viscous force is called
A. Reynold's number
B. Froude's number
C. Weber's number
D. Euler's number
Answer : A

41. To avoid an interruption in the flow of a siphon, an air vessel is provided
A. At the inlet
B. At the outlet
C. At the summit
D. At any point between inlet and outlet
Answer : C

42. The point in the immersed body through which the resultant pressure of the liquid may be taken to act is known as
A. Meta center
B. Center of pressure
C. Center of buoyancy
D. Center of gravity
Answer : B

43. 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

44. 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

45. 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

46. The total energy of a liquid particle in motion is equal to
A. Pressure energy + kinetic energy + potential energy
B. Pressure energy - (kinetic energy + potential energy)
C. Potential energy - (pressure energy + kinetic energy
D. Kinetic energy - (pressure energy + potential energy)
Answer : A

47. Which of the following instrument can be used for measuring speed of an aeroplane?
A. Venturimeter
B. Orifice plate
C. Pitot tube
D. Rotameter
Answer : C

48. A manometer is used to measure
A. Low pressure
B. Moderate pressure
C. High pressure
D. Atmospheric pressure
Answer : C

49. One stoke is equal to
A. 10^-2 m²/s
B. 10^-3 m²/s
C. 10^-4 m²/s
D. 10^-6 m²/s
Answer : C

50. The coefficient of discharge in case of internal mouthpiece is __________ that of external mouthpiece.
A. Less than
B. More than
C. Equal to
D. None of these
Answer : A