Category: Fluid Mechanics Objective Questions

250+ TOP MCQs on Navier-Stokes Equations of Motion and Answers

Fluid Mechanics Multiple Choice Questions on “Navier-Stokes Equations of Motion”.

1. Navier- Stokes equation describes the motion of __________
a) Solid substance
b) Non-viscous fluid
c) Viscous fluid
d) Gas
Answer: c
Clarification: The equation described by Navier- Stokes is for a viscous fluid. The balanced equation arises from Newton’s Second Law of fluid motion. It assumes that the stress in the fluid is equal to the sum of a diffusing viscous term and a pressure term.

2. Froude number depends upon_________
a) Flow velocity, external field and characteristic length
b) Flow velocity and mass
c) Mass flow rate and volume
d) Characteristic length and volume
Answer: a
Clarification: The Froude number is a dimensionless number. It is defined as the ratio of flow inertia to the external field. The Froude number is based on the speed-length ratio.

3. Continuum mechanics is a branch of mechanics that deals with________
a) Fluid particles
b) Discrete particles
c) Kinematics and mechanical behaviour
d) Hydrostatic Pressure
Answer: c
Clarification: Continuum mechanics is a branch that deals with the analysis of kinematics and mechanical behaviour of materials. It can be modelled as a continuous mass rather than as discrete particles.

4. Which among the following cannot be used as an alternative term for a “solenoidal vector field”?
a) Incompressible vector field
b) Divergence- free vector field
c) Transverse vector field
d) Continuous random field
Answer: d
Clarification: A random field comes under a stochastic process. It can take up values that are multidimensional vectors or points on some manifold. A random field is a list of random numbers whose indices are identified with a discrete set of points in space.

5. The Navier- Stokes equation can be used in which of the following applications?
a) Automobiles
b) Ocean Currents
c) Airplanes
d) Thermometer
Answer: b
Clarification: An ocean current is a continuous direct movement of seawater. Ocean currents are forces generated by acting upon the mean flow. Therefore, ocean currents satisfy Navier-Stokes equation as they have a primary horizontal water movement.

6. Which among the following is not an example of magneto fluids?
a) Plasma
b) Liquid metals
c) Salt water
d) Alcohol
Answer: d
Clarification: Alcohol is an organic compound on which a hydroxyl functional group is bounded to a saturated carbon atom. Alcohols work as an antifreeze solution at cool temperatures. Thus, it is not a magneto fluid.

7. What is the velocity profile for Poiseuille flow?
a) Zero
b) Constant
c) Linear
d) Quadratic
Answer: d
Clarification: The velocity profile for Poiseuille flow is zero at either side of the channel and non-zero in the middle. Therefore, Quadratic equation is the only possible option here.

8. What are the Newtonian constitutive assumptions regarding relationship between stress tensor and velocity gradients?
a) Linear and isotropic
b) Constant
c) Linear
d) Non-Uniform
Answer: a
Clarification: Newtonian fluid is a fluid in which the viscous stresses arise due to its flow. The flow experiences a strain rate at every point. The strain rate is related to the constant viscosity tensor that does not depend upon the stress and velocity of the flow. Thus, the relationship is linear and isotropic.

9. What is the incompressibility condition in Navier-Stokes equation?
a) ∇.u=0
b) ∇.u>0
c) ∇.u<0
d) ∇.u=1
Answer: a
Clarification: This comes from the relation between the divergence of the flow. It also relates the Jacobian transformation with Lagrangian and Eulerian coordinates. Thus, ∇.u=0.

10. The velocity profile of the Couette flow is _______
a) Quadratic
b) Constant
c) Linear
d) Zero
Answer: c
Clarification: Couette flow is a flow of viscous fluid in the space between two surfaces. One surface moves tangentially with respect to the other. The configuration often takes the form of the two parallel plates or the gaps in between two cylinders.

250+ TOP MCQs on Methods of Determination of Coefficient of Viscosity and Answers

Fluid Mechanics Multiple Choice Questions on “Methods of Determination of Coefficient of Viscosity”.

1. What is the unit of coefficient of viscosity?
a) kgsm-2
b) kgms-2
c) Nms-2
d) Nsm-2
Answer: d
Clarification: Coefficient of viscosity is defined as the degree to which the fluid resists flow under an applied force. It is expressed as ratio of shearing stress to the velocity gradient. The unit is Nsm-2.

2. What happens to the coefficient of viscosity if the temperature increases?
a) Increases
b) Decreases
c) Remains the same
d) Independent of temperature
Answer: b
Clarification: With the increase in temperature, the coefficient of viscosity of fluid decreases. This happens due to the weakening of bonds between the molecules. Because of its dash pot coefficient, the flow attains peak deformation.

3. What is the magnitude of the coefficient of viscosity?
a) Frictional force/Area
b) Frictional force/ (Area* velocity gradient)
c) Frictional force*Area
d) Frictional force*Area/ velocity gradient
Answer: b
Clarification: Coefficient of viscosity is defined as the degree to which the fluid resists flow under an applied force. It is expressed as a ratio of shearing stress to the velocity gradient. It has a unit of Nsm-2.

4. Which among the following methods are not standard laboratory viscometers?
a) Saybolt Viscometer
b) Redwood Viscometer
c) Ostwald Viscometer
d) Vibrational viscometer
Answer: d
Clarification: Vibrational viscometer is a viscometer that serves the same purpose as the other viscometers. But, it is not used for laboratory purposes. It measures the damping oscillations using a resonator immersed in a fluid.

5. What is the formula for coefficient of static friction?
a) R/F
b) F*R
c) F/R
d) F+R
Answer: c
Clarification: Coefficient of static friction is defined as the ratio of limiting frictional force to the normal reaction force. Limiting frictional force is denoted by ‘F’ and normal frictional force is denoted by ‘R’. Therefore, option ‘c’ is correct.

6. What is the dimension for coefficient of friction?
a) [M][L][T]
b) [M][L][T]2
c) It has no dimensions
d) [M][L]-1[T]-1
Answer: c
Clarification: Coefficient of static friction is defined as the ratio of limiting frictional force to the normal reaction force. Dividing the dimensions of the limiting frictional force and normal frictional force, the units cancel out each other due to which it has no dimensions.

7. Where is friction a drawback?
a) On roads
b) On pipes
c) Staircase
d) Playground
Answer: b
Clarification: Friction in pipes lead to major and minor loses. It is an economic significance. It provides a lot of confusions on whether the pipe or duct is entirely closed. It leads to a high amount of power loss in drawing fluid through the pipes.

8. Measuring the coefficient of static friction takes place by_________
a) Tilting two objects
b) Keeping it stationery
c) Reciprocating
d) Rotating
Answer: a
Clarification: The easiest way to measure the coefficient of static friction is by placing the two objects together and tilting them until one object slides over the other. Coefficient is related to the angle at which one object starts to slide over the other.

9. Coefficient of kinetic friction can be found out by inclined plane method and horizontal plane method.
a) True
b) False
Answer: a
Clarification: Coefficient of kinetic friction can be found out by inclined plane method and horizontal plane method. In case of inclined plane, the block slides down on an incline with a constant velocity. In the horizontal plane method, the block does not slide and produces nil friction.

10. Which among the following is used to determine the angle of repose?
a) Horizontal plane method
b) Tilting box method
c) Fixed funnel method
d) Revolving cylinder method
Answer: a
Clarification: Angle of repose is defined as the steepest angle of descent or dip. It is with relation to the horizontal plane to which a material can be piled. Example: When we pile up stones one over the other, the stones tend to slide along the heap at a certain point. The angle at that point is the angle of repose.

11. What is the maximum value for the angle of repose?
a) 30
b) 60
c) 90
d) 180
Answer: c
Clarification: Angle of repose is defined as the steepest angle of descent or dip. It is with relation to the horizontal plane to which a material can be piled. The maximum value for the angle of repose is 90 degrees. It is exactly perpendicular to the horizontal surface.

12. What is the minimum value for angle of repose?
a) 0
b) 60
c) 90
d) 180
Answer: a
Clarification: Angle of repose is defined as the steepest angle of descent or dip. It is with relation to the horizontal plane to which a material can be piled. The minimum value for angle of repose is zero degrees. It lies on the horizontal surface. Therefore, there is no sliding.

250+ TOP MCQs on Dimensionless Numbers and Answers

Fluid Mechanics Multiple Choice Questions on “Dimensionless Numbers”.

1. The rate at which the particles of fluid can spread is called_______
a) Surface tension
b) Diffusivity
c) Viscosity
d) Kinetics
Answer: b
Clarification: Diffusivity is defined as the rate of diffusion. It is a measure of particles at which the fluids or heat can spread. They are measured in different mediums. It can be defined on the basis of its properties.

2. Which among the following is the standard symbol for Archimedes number?
a) A
b) AR
c) Ar
d) a
Answer: c
Clarification: The standard symbol for Archimedes number is Ar. Archimedes number in fluid mechanics deals with the motion of fluids. This takes place due to the differences in their densities. It was followed by the Archimedes principle.

3. The Prandtl Number approximates ___________
a) Momentum diffusivity to thermal diffusivity
b) Thermal diffusivity to momentum diffusivity
c) Shear stress to thermal diffusivity
d) Thermal diffusivity to kinematic viscosity
Answer: a
Clarification: The Prandtl number is a dimensionless number. It approximates the ratio of momentum diffusivity to thermal diffusivity. It can be expressed as Pr = v/ α(1). Where α= thermal diffusivity and v= momentum diffusivity.

4. Which among the following is the standard symbol for Atwood number?
a) A
b) AR
c) Ar
d) a
Answer: a
Clarification: The standard symbol for Atwood number is A. Atwood’s number in fluid mechanics deals with the onset of instabilities in mixtures of fluid. It is due to the density differences in fluid.

5. Which among the following is the standard symbol for Blake number?
a) Bi
b) ba
c) Bl
d) b
Answer: b
Clarification: The standard symbol for Blake number is B or Bl. Blake number in fluid mechanics deals with geology, fluid mechanics and porous media. It is due to the inertial over the viscous forces in fluid flow through porous media.

6. Which among the following is the standard symbol for Darcy friction factor?
a) F
b) Fd
c) C
d) Cd
Answer: b
Clarification: The standard symbol for Darcy friction factor is Fd. Darcy friction factor in fluid mechanics deals with fractions of pressure losses. This is due to the development of friction in the pipe.

7. Fanning friction factor is _________
a) 0.25 times Darcy friction factor
b) Same as Darcy friction factor
c) 2 times Darcy friction factor
d) Independent
Answer: a
Clarification: Fanning friction factor is 0.25 times Darcy friction factor. Fanning friction factor in fluid mechanics deals fraction of pressure losses due to friction in the pipe.

8. Which among the following is the standard symbol for Froude number?
a) F
b) Fo
c) Fr
d) f
Answer: c
Clarification: The standard symbol for Froude number is Fr. Froude number in fluid mechanics deals with wave and surface behaviour of fluid particles. This is with the ratio of body’s inertia to gravitational forces.

9. Which among the following is the standard symbol for Peclet number?
a) P
b) p
c) Pe
d) pe
Answer: c
Clarification: The standard symbol for Peclet’s number is Pe. Peclet’s number in fluid mechanics deals with heat transfer. It is defined as the ratio of transport rate over molecular diffusive transport.

10. Which among the following is the formula for Knudsen number?
a) λ⁄L
b) λ⁄2L
c) λ⁄3L
d) λ⁄4L
Answer: a
Clarification: The formula for Knudsen number is λ⁄L. Knudsen number in fluid mechanics deals with gas dynamics. It is defined as the ratio of the molecular mean free path length to the representative scale length.

250+ TOP MCQs on Chezy’s Equation and Answers

Fluid Mechanics Multiple Choice Questions on “Chezy’s Equation”.

1. Calculate the discharge through a channel having a bed slope 1 in 1000, area 12m2, hydraulic radius of 1.2m and Chezy’s constant being equal to 50.
a) 17.98 m3/s
b) 18.98 m3/s
c) 19.98 m3/s
d) 20.98 m3/s
Answer: d
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q1

2. What is the dimension of C?
a) LT
b) L1/2 T-1
c) LT-1
d) L-1 T-1
Answer: b
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q2

3. The depth and widths of a rectangular channel are 2m and 5m respectively, calculate the discharge of water through the channel if the bed slope is 1 in 500 and Chezy’s constant being 60.
a) 28.27 m3/s
b) 38.27 m3/s
c) 48.27 m3/s
d) 58.27 m3/s
Answer: a
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q3

4. Estimate the discharge of water through a triangular channel having depth 3m, side slope1H:2V, the bed slope is 1 in 500 and C=60.
a) 14.48 m3/s
b) 15.48 m3/s
c) 16.48 m3/s
d) 17.48 m3/s
Answer: c
fluid-mechanics-questions-answers-chezys-equation-q4

5. The discharge of water through a trapezoidal channel is 1.5 m3/s, the base width of the channel is 7m, the depth is 2m and the side slope is 1H:3V. Bed slope is 1 in 2000, determine the value of the Chezy’s constant.
a) 50
b) 55
c) 60
d) 65
Answer: c
Clarification: fluid-mechanics-questions-answers-chezys-equation-q5

6. Find the discharge through a circular channel section having diameter of 5m, the value of Chezy’s constant is 90 and the bed slope is 1 in 4000.
a) 13.61 m3/s
b) 14.61 m3/s
c) 15.61 m3/s
d) 16.61 m3/s
Answer: c
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q6

7. The discharge through a rectangular channel is 16.62 m3/s and the wetted area is equal to 12m2. The width of the channel is 6m and the bed slope is 1 in 1000, calculate the value of the Chezy’s constant.
a) 35
b) 40
c) 45
d) 50
Answer: b
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q7

8. Calculate the discharge through a triangular channel having a normal depth of 4m, wetted area equalling to 8m2 and having side slope and bed slopes 1/2 and 1 in 500 respectively. C = 40.
a) 13.54 m3/s
b) 14.54 m3/s
c) 15.54 m3/s
d) 16.54 m3/s
Answer: a
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q8

9. The perimeter of a circular channel section is 18.84m, calculate the discharge through the channel when it is running full having a bed slope of 1 in 1500 and C = 60.
a) 53.62 m3/s
b) 63.62 m3/s
c) 73.62 m3/s
d) 83.62 m3/s
Answer: a
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q9

10. The discharge through a trapezoidal channel is 61 m3/s and the depth and widths of the channel are 4m and 5m respectively. The wetted perimeter of the channel is 13.16m, calculate the bed slope of the channel if the value of C is 45.
a) 1 in 500
b) 1 in 1000
c) 1 in 1500
d) 1 in 2000
Answer: a
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q10

11. The velocity of flow through a channel is 0.74 m/s and the hydraulic radius of the channel is 1.11m, calculate the value of C if the bed slope of the channel is 1 in 5000.
a) 40
b) 45
c) 50
d) 55
Answer: c
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q11

12. Estimate the discharge through a channel having area 24m2 and perimeter 16m if the bed slope of the channel is equal to 1 in 1000 and C = 70.
a) 62 m3/s
b) 63 m3/s
c) 64 m3/s
d) 65 m3/s
Answer: d
Clarification:
fluid-mechanics-questions-answers-chezys-equation-q12

250+ TOP MCQs on Vapor Pressure and Answers

Fluid Mechanics Multiple Choice Questions on “Vapor Pressure”.

1. Which of the following statement is true about vapor pressure of a liquid?
a) Vapor pressure is closely related to molecular activity and temperature of the liquid
b) Vapor pressure is closely related to molecular activity but independent of the temperature of the liquid
c) Vapor pressure is not affected by molecular activity and temperature of the liquid
d) Vapor pressure is not affected by molecular activity and is independent of the temperature of the liquid

Answer: a
Clarification: The vapor pressure of a liquid at a given temperature is given by the pressure ex-erted by the saturated vapor on the liquid surface. When the vapor is saturated, an equilibrium exists between the liquid and the vapor phases. The number of molecules leaving the liquid surface is equal to the number of molecules entering the liquid surface. Hence, it is obvious that vapor pressure will be related to molecular activity and consequently to temperature. With the increase in temperature molecular activity increases as a result of which vapor pressure increases.

2. Which of the following equation correctly depicts the relation between the vapor pressure of a liquid and it’s temperature?
a) Vapor pressure increases linearly with the increase in temperature of the liquid
b) Vapor pressure increases slightly with the increase in temperature of the liquid at low temperatures and the rate of increase goes high at higher temperatures
c) Vapor pressure increases rapidly with the increase in temperature of the liquid at low temperatures and the rate of increase goes low at higher temperatures
d) Vapor pressure remains unchanged with the increase in temperature of the liquid

Answer: b
Clarification: Vapor pressure is closely related to molecular activity which is in turn dependant on the temperature of the liquid. With the increase in temperature molecular activity of a vapor increases slowly at first and then rapidly. Similar is the nature of variaion of vapor pressure.

3. Which of the following is the condition for the boiling of a liquid?
a) Absolute pressure of a liquid must be greater than or equal to it’s vapor pressure
b) Absolute pressure of a liquid must be less than or equal to it’s vapor pressure
c) Absolute pressure of a liquid must be equal to it’s vapor pressure
d) Absolute pressure of a liquid must be greater than it’s vapor pressure

Answer: b
Clarification: As the absolute pressure of a liquid goes below it’s vapor pressure, the formation of vapor bubbles start. Thus, for boiling to start, the absolute pressure of a liquid must be less than or equal to it’s vapor pressure.

4. Which of the following machines have the possibility of cavitation?
a) Reaction turbines and centrifugal pumps
b) Reaction turbines and reciprocating pumps
c) Impulse turbines and centrifugal pumps
d) Impulse turbines and reciprocating pumps

Answer: a
Clarification: Cavitation occurs whenever absolute pressure of a liquid drops below it’s vapor pressure. Dropping of pressure is observed mainly in reaction turbines and centrifugal pumps.

5. The three liquids 1, 2, and 3 with vapor pressures V1, V2 and V3 respectively, are kept under same pressure. If V1 > V2 > V3, which liquid will start boiling early?
a) liquid 1
b) liquid 2
c) liquid 3
d) they will start boiling at the same time

Answer: a
Clarification: A liquid starts to boil whenever it’s absolute pressure drops below it’s vapor pressure. Thus, the absolute pressure of liquid 1 will drop early, as a result it’ll start boiling early.

6. Equal amount of a particular liquid is poured into three similar containers, namely 1, 2 and 3, at a temperature of T1, T2 and T3 respectively. If T1 < T2 < T3, the liquid in which container will have the highest vapor pressure?
a) container 1
b) container 2
c) container 3
d) the vapor pressure of the liquid will remain the same irrespective of it’s temperature

Answer: c
Clarification: Higher the temperature, higher is the molecular activity and consequently, higher is the vapor pressure of a given liquid. Since, container 3 is at the highest temperature, liquid in it will have the highest vapor pressure.

7. The absolute pressure of a water is 0.5kN above it’s vapor pressure. If it flows with a velocity of 1m/s, what will be the value of Cavitation Number describing the flow induced boiling?
a) 0.25
b) 0.5
c) 1
d) 2

Answer: c

8. Which of the following is correct regarding the formation and collapse of vapor bubbles in a liquid?
a) Vapor bubbles are formed when the fluid pressure goes above the vapor pressure and collapses when the fluid pressure goes above the bubble pressure
b) Vapor bubbles are formed when the fluid pressure goes above the vapor pressure and collapses when the fluid pressure goes below the bubble pressure
c) Vapor bubbles are formed when the fluid pressure drops below the vapor pressure and collapses when the fluid pressure goes below the bubble pressure
d) Vapor bubbles are formed when the fluid pressure drops below the vapor pressure and collapses when the fluid pressure goes above the bubble pressure

Answer: d
Clarification: Whenever the absolute pressure of a fluid drops below it’s vapor pressure, bubble formation starts. Again, when the fluid pressure goes above the bubble pressure, it’ll collapse. This is how cavitation formation takes place.

250+ TOP MCQs on Bouyancy and Answers

Fluid Mechanics Multiple Choice Questions on “Bouyancy”.

1. Find the position of centre of buoyancy for a wooden block of width 3.5 m and depth 1 m, when it floats horizontally in water. The density of wooden block id 850 kg/m3 and its length 7.0 m.
a) 0.95
b) 0.85
c) 1.05
d) 1.65
Answer: b
Clarification: Weight of the block=ρ*g*Volume=850*9.81*7*3.5*1=204.29 kN
Volume of
water displaced= Weight of water displaced/weight density of water
= 20.825 m3.
h=20.825/3.5*7=0.85 m.

2. A stone weighs 450 N in air and 200 N in water. Compute the volume of stone.
a) .025 m3
b) .05 m3
c) .075 m3
d) None of the mentioned
Answer: a
Clarification: Weight of water displaced=Weight of stone in air – Weight of stone in water
=250
Volume of water displaced=Volume of stone=250/9.81*1000=0.025 m3.

3. A stone weighs 650 N in air and 275 N in water. Compute its specific gravity.
a) 1.73
b) 2.45
c) 3.46
d) 0.865
Answer: a
Clarification: Weight of water displaced=Weight of stone in air – Weight of stone in water
=375
Volume of water displaced=Volume of stone=375/9.81*1000=0.038 m3
Density of stone= mass/volume=650/9.81*0.038=1733 kg/m3
specific gravity= Density of stone/Density of water=1.73.

4. A body of dimensions 2.7 m * 3.8 m * 2.5 m, weighs 2500 N in water.Find its weight in air.
a) 254.12 kN
b) 508.25 kN
c) 101.65 kN
d) 127.06 kN
Answer: a
Clarification: Weight of stone in air = Weight of water displaced+Weight of stone in water
= 9.81*1000*2.7*3.8*2.5+2500=254.12 kN.

5. Find the density of metallic body which floats at the interface of mercury of sp.gr 13.6 and water such that 40 % of its volume is sub-merged in mercury and 60% in water.
a) 6040 kg/m3
b) 12080 kg/m3
c) 24160 kg/m3
d) 3020 kg/m3
Answer: a
Clarification: Total Bouyant force=Force of bouyancy due to water+Force of bouyancy due to mercury
For equilibrium, Total bouyant force= Weiht of body
1000*9.81*0.6*V + 13.6*1000*9.81*0.4*V=ρ*g*V
ρ=6040 kg/m3.

6. What is the principal cause of action of buoyant force on a body submerged partially or fully in fluid?
a) Displacement of fluid due to submerged body
b) Development of force due to dynamic action
c) Internal shear forces mitigating external forces
d) None of the mentioned
Answer: a
Clarification: The principal cause of action of buoyant force on a body submerged partially or fully in fluid is the force equal in magnitude to the weight of the volume of displaced fluid.

7. How can relatively denser object be made to float on the less dense fluid?
a) By altering the shape.
b) By altering the forces acting on the object
c) By altering the shear forces acting on the object
d) None of the mentioned
Answer: a
Clarification: By changing the shape of an object it can be made to float on a fluid even if it is denser than that fluid. This principle is used in ship building.

8. What happens to the buoyant force acting on the airship as it rises in the air?
a) Buoyant force increases
b) Buoyant force decreases
c) Buoyant force remains constant
d) Buoyant force first increases then shows decrease
Answer: b
Clarification: Buoyant force acting on the airship decreases as it rises in the air as air at higher altitude becomes rarer and its density decreases.

9. As a balloon rises in the air its volume increases, at the end it acquires a stable height and cannot rise any further.
a) True
b) False
Answer: a
Clarification: As balloon rises in air, pressure acting on it reduces and therefore its volume increases. Also, a rising balloon ceases rising when it and the displaced air are equal in weight.

10. Submarines use principle of ‘neutral buoyancy’ to go into the water.
a) True
b) False
Answer: a
Clarification: To dive, the submarine tanks are opened to allow air to exhaust, while the water flows in. When the weight has been balanced so the overall density of the submarine is equal to the water around it, it has neutral buoyancy and hence will go down.