Fluid Mechanics MCQs

1. Fluid mechanics is the study of:
a) Gases only
b) Liquids only
c) Both gases and liquids
d) Solids only
Answer: c) Both gases and liquids

2. The unit of dynamic viscosity in the SI system is:
a) Pascal
b) Poise
c) Pascal-second
d) Newton-second
Answer: c) Pascal-second

3. The property of a fluid which offers resistance to deformation is called:
a) Density
b) Viscosity
c) Pressure
d) Surface tension
Answer: b) Viscosity

4. The continuity equation is based on the principle of:
a) Conservation of mass
b) Conservation of energy
c) Conservation of momentum
d) Conservation of pressure
Answer: a) Conservation of mass

5. The equation of continuity for an incompressible fluid flow is:
a)
𝐴
1
𝑉
1
=
𝐴
2
𝑉
2
A
1

V
1

=A
2

V
2

b)
𝐴
1
2
𝑉
1
=
𝐴
2
2
𝑉
2
A
1
2

V
1

=A
2
2

V
2

c)
𝐴
1
𝑉
1
2
=
𝐴
2
𝑉
2
2
A
1

V
1
2

=A
2

V
2
2

d)
𝐴
1
𝑉
1
3
=
𝐴
2
𝑉
2
3
A
1

V
1
3

=A
2

V
2
3

Answer: a)
𝐴
1
𝑉
1
=
𝐴
2
𝑉
2
A
1

V
1

=A
2

V
2

6. Bernoulli’s equation is based on the principle of:
a) Conservation of mass
b) Conservation of energy
c) Conservation of momentum
d) Conservation of pressure
Answer: b) Conservation of energy

7. In Bernoulli’s equation, the sum of pressure energy, kinetic energy, and potential energy per unit weight is:
a) Constant
b) Variable
c) Dependent on time
d) Dependent on velocity
Answer: a) Constant

8. The Bernoulli’s equation is applicable to:
a) Viscous and compressible fluids
b) Inviscid and incompressible fluids
c) Compressible fluids only
d) Viscous fluids only
Answer: b) Inviscid and incompressible fluids

9. The pressure at a point in a fluid at rest is called:
a) Static pressure
b) Dynamic pressure
c) Total pressure
d) Stagnation pressure
Answer: a) Static pressure

10. The Venturi meter is used to measure:
a) Pressure
b) Flow rate
c) Velocity
d) Viscosity
Answer: b) Flow rate

11. The phenomenon of vapor bubbles forming in a flowing liquid and then collapsing is called:
a) Cavitation
b) Lamination
c) Turbulence
d) Sublimation
Answer: a) Cavitation

12. A streamline is defined as a line:
a) Tangential to the velocity vector at every point
b) Normal to the velocity vector at every point
c) Along which the velocity is constant
d) Along which the pressure is constant
Answer: a) Tangential to the velocity vector at every point

13. The Reynolds number is the ratio of:
a) Inertial forces to viscous forces
b) Viscous forces to inertial forces
c) Pressure forces to viscous forces
d) Viscous forces to pressure forces
Answer: a) Inertial forces to viscous forces

14. The flow of fluid is called laminar if the Reynolds number is:
a) Less than 2000
b) Between 2000 and 4000
c) Greater than 4000
d) Greater than 6000
Answer: a) Less than 2000

15. The flow of fluid is called turbulent if the Reynolds number is:
a) Less than 2000
b) Between 2000 and 4000
c) Greater than 4000
d) Greater than 6000
Answer: c) Greater than 4000

16. The flow in which the fluid particles follow a random path is called:
a) Laminar flow
b) Turbulent flow
c) Uniform flow
d) Steady flow
Answer: b) Turbulent flow

17. The head loss in a pipe due to friction is given by:
a) Darcy-Weisbach equation
b) Bernoulli’s equation
c) Continuity equation
d) Euler’s equation
Answer: a) Darcy-Weisbach equation

18. The Hagen-Poiseuille equation is valid for:
a) Turbulent flow
b) Laminar flow
c) Compressible flow
d) Supersonic flow
Answer: b) Laminar flow

19. The point in the immersed body through which the resultant pressure of the liquid may be taken to act is known as:
a) Center of pressure
b) Center of gravity
c) Center of buoyancy
d) Metacenter
Answer: a) Center of pressure

20. The buoyant force on a submerged object is equal to:
a) Weight of the object
b) Volume of the object
c) Weight of the fluid displaced by the object
d) Volume of the fluid displaced by the object
Answer: c) Weight of the fluid displaced by the object

21. The dimensionless number which represents the effect of compressibility is:
a) Reynolds number
b) Froude number
c) Mach number
d) Weber number
Answer: c) Mach number

22. The term “viscosity” refers to a fluid’s:
a) Density
b) Resistance to flow
c) Pressure
d) Buoyancy
Answer: b) Resistance to flow

23. The ratio of inertial forces to gravitational forces is called:
a) Reynolds number
b) Froude number
c) Mach number
d) Weber number
Answer: b) Froude number

24. The flow in which the fluid properties vary with time at any given location is called:
a) Steady flow
b) Unsteady flow
c) Uniform flow
d) Non-uniform flow
Answer: b) Unsteady flow

25. The instrument used to measure the velocity of flow is:
a) Manometer
b) Pitot tube
c) Orifice meter
d) Venturi meter
Answer: b) Pitot tube

26. The term “hydraulic diameter” is used for:
a) Circular pipes only
b) Non-circular pipes only
c) Both circular and non-circular pipes
d) Open channels only
Answer: c) Both circular and non-circular pipes

27. The critical velocity of a fluid in a pipe depends on:
a) Diameter of the pipe
b) Density of the fluid
c) Viscosity of the fluid
d) All of the above
Answer: d) All of the above

28. The ratio of the actual velocity of fluid to the velocity of sound in the fluid is called:
a) Reynolds number
b) Froude number
c) Mach number
d) Weber number
Answer: c) Mach number

29. The dimensionless number which represents the effect of surface tension is:
a) Reynolds number
b) Froude number
c) Mach number
d) Weber number
Answer: d) Weber number

30. The streamline and equipotential lines in a flow field:
a) Are parallel to each other
b) Are perpendicular to each other
c) Intersect at 45 degrees
d) Intersect at 30 degrees
Answer: b) Are perpendicular to each other

31. The Navier-Stokes equation deals with the law of conservation of:
a) Mass
b) Energy
c) Momentum
d) Pressure
Answer: c) Momentum

32. The phenomenon by which a fluid rises in a thin tube due to surface tension is called:
a) Adhesion
b) Capillarity
c) Cohesion
d) Viscosity
Answer: b) Capillarity

33. The potential flow theory is based on the assumption that the fluid is:
a) Compressible
b) Incompressible
c) Viscous
d) Inviscid
Answer: d) Inviscid

34. The line joining the points of highest water elevation in open channel flow is known as:
a) Streamline
b) Equipotential line
c) Hydraulic grade line
d) Energy grade line
Answer: d) Energy grade line

35. The phenomenon by which the boundary layer separates from the surface is known as:
a) Boundary layer transition
b) Boundary layer separation
c) Boundary layer adhesion
d) Boundary layer cohesion
Answer: b) Boundary layer separation

36. The flow rate through an orifice is given by:
a) Bernoulli’s equation
b) Continuity equation
c) Torricelli’s theorem
d) Navier-Stokes equation
Answer: c) Torricelli’s theorem

37. In a fluid flow, the condition where no slip occurs at the boundary is known as:
a) Slip condition
b) No-slip condition
c) Boundary condition
d) Continuity condition
Answer: b) No-slip condition

38. The height to which a liquid will rise in a capillary tube is inversely proportional to:
a) Diameter of the tube
b) Surface tension
c) Viscosity
d) Density
Answer: a) Diameter of the tube

39. The dimensionless number which represents the ratio of inertia force to viscous force is:
a) Reynolds number
b) Froude number
c) Mach number
d) Weber number
Answer: a) Reynolds number

40. The most economical section of a rectangular channel is one for which the ratio of width to depth is:
a) 1
b) 2
c) 3
d) 4
Answer: b) 2

41. The pressure measured with respect to the absolute vacuum is called:
a) Gauge pressure
b) Absolute pressure
c) Atmospheric pressure
d) Static pressure
Answer: b) Absolute pressure

42. The discharge over a rectangular weir is given by:
a)
𝑄
=
2
3
𝐶
𝑑
2
𝑔
𝐿
ℎ
3
/
2
Q=
3
2

Cd
2g

Lh
3/2

b)
𝑄
=
𝐶
𝑑
2
𝑔
𝐿
ℎ
Q=Cd
2g

Lh
c)
𝑄
=
𝐶
𝑑
2
𝑔
𝜋
𝐷
ℎ
2
Q=Cd
2g

πDh
2

d)
𝑄
=
1
2
𝐶
𝑑
2
𝑔
𝐿
ℎ
3
/
2
Q=
2
1

Cd
2g

Lh
3/2

Answer: a)
𝑄
=
2
3
𝐶
𝑑
2
𝑔
𝐿
ℎ
3
/
2
Q=
3
2

Cd
2g

Lh
3/2

43. In open channel flow, the specific energy is the:
a) Total energy per unit discharge
b) Total energy per unit weight of fluid
c) Energy per unit volume
d) Energy per unit length
Answer: b) Total energy per unit weight of fluid

44. The boundary layer thickness is defined as the distance from the boundary where the velocity reaches:
a) 50% of the free stream velocity
b) 90% of the free stream velocity
c) 95% of the free stream velocity
d) 99% of the free stream velocity
Answer: d) 99% of the free stream velocity

45. The property of fluid which enables it to resist tensile stress is called:
a) Viscosity
b) Density
c) Surface tension
d) Cohesion
Answer: c) Surface tension

46. The depth of flow in an open channel corresponding to minimum specific energy is called:
a) Normal depth
b) Critical depth
c) Subcritical depth
d) Supercritical depth
Answer: b) Critical depth

47. The point at which the resultant pressure on a submerged body acts is called:
a) Center of gravity
b) Center of pressure
c) Center of buoyancy
d) Metacenter
Answer: b) Center of pressure

48. The flow through a nozzle is:
a) Subsonic
b) Supersonic
c) Both subsonic and supersonic
d) Neither subsonic nor supersonic
Answer: c) Both subsonic and supersonic

49. The hydraulic radius is defined as the ratio of:
a) Area of flow to wetted perimeter
b) Wetted perimeter to area of flow
c) Velocity of flow to area of flow
d) Area of flow to velocity of flow
Answer: a) Area of flow to wetted perimeter

50. The velocity distribution for turbulent flow through a closed conduit is:
a) Parabolic
b) Logarithmic
c) Linear
d) Hyperbolic
Answer: b) Logarithmic

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