Category: Fluid Mechanics Objective Questions

250+ TOP MCQs on Pressure at a Point in Compressible Fluid and Answers

Fluid Mechanics Multiple Choice Questions on “Pressure at a Point in Compressible Fluid”.

1. If the atmospheric pressure at sea level is 7.5 N/cm2, determine the pressure at a height of 3000m assuming the pressure variation follows isothermal law. The density of air is given as 1.2 km/m3.
a) 4.68 N/cm2
b) 9.37 N/cm2
c) 2.34 N/cm2
d) None of the mentioned

Answer: a
Clarification: pressure at any height Z = p*e-gZ/RT
=75000*e -9.81*3000*1.2/75000
= 4.68 N/cm2.

2. The barometric pressure at sea level is 760 mm of Mercury while that on a mountain top is 715 mm. If the density of air is assumed constant at 1.2 kg/m3 , what is the elevation of the mountain top?
a) 510 m
b) 1020 m
c) 255 m
d) 128 m

Answer: a
Clarification: Gauge pressure at any height h = pressure at sea level – pressure at that height
h=(9.81*13600*0.76)-9.81*13600*0.715)/1.2*9.81
=510 m.

3. Calculate the pressure at a height of 6500m above the sea level if the atmospheric pressure is 10.145 N/cm2 and temperature is 25℃ assuming air is incompressible. Take density of air as 1.2 kg/m3. Neglect variation of g.
a) 4.98 N/cm2
b) 2.49 N/cm2
c) 1.24 N/cm2
d) None of the mentioned

Answer: b
Clarification: Pressure= p – density of air*g*height
=101450-9.81*1.2*6500
= 2.49 N/cm2.

4. Calculate the pressure of air at a height of 3500m from sea level where pressure and temperature of air are 10 N/cm2 and 25℃ respectively. The temperature lapse rate is given as 0.0065 ℃ /m. Take density of air at sea level equal to 1.2 kg/m3.
a) 19.7 N/cm2
b) 9.85 N/cm2
c) 4.93 N/cm2
d) 6.24 N/cm2

Answer: b
Clarification: pressure=p * (1-(k-1/k)*g*h*density/p)k/(k-1)
=9.85 N/cm2

Here, Lapse rate= -g/R*(k/k-1).

5. Pressure variation for compressible fluid is maximum for which kind of process?
a) Isothermal
b) Adiabatic
c) Quasi Static
d) None of the mentioned

Answer: a
Clarification: Due to constant temperature, pressure variation for compressible fluid is maximum for isothermal process.

6. Why can’t the density be assumed as constant for compressible fluids?
a) It shows variation with temperature and pressure
b) It remains constant with temperature and pressure
c) It becomes almost constant at very high temperature
d) None of the mentioned

Answer: a
Clarification: Volume and hence density changes with change in temperature and pressure.

7.What is the variation observed in temperature in atmosphere with respect to elevation?
a) It goes on decreasing with height
b) It goes on increasing with height
c) It first increases then decreases
d) It first decreases then increases

Answer: d
Clarification: It goes on decreasing first and shows increase after 32000 m.

8. As we go upwards, at height there is slight decrease in pressure variation.
a) True
b) False

Answer: a
Clarification: There is slight decrease in pressure as value of g (acceleration due to gravity) decreases slightly as we go higher.

9. For dynamic fluid motion in a pipe, the pressure measurement cannot be carried out accurately by manometer.
a) True
b) False

Answer: a
Clarification: For fluid moving with variable velocity, fluctuation in pressure is frequent and more in magnitude. Hence, we cannot use manometer.

10. A simple U tube manometer connected to a pipe in which liquid is flowing with uniform speed will give which kind of pressure?
a) Absolute Pressure
b) Vacuum Pressure
c) Gauge Pressure
d) None of the mentioned

Answer: c

250+ TOP MCQs on Important Cases of Potential Flow and Answers

Fluid Mechanics online test on “Important Cases of Potential Flow”.

1. The characteristic of Ideal fluid are
a) Incompressible
b) Inviscid
c) Fluid velocity is uniform
d) Shear stress has a constant, non zero value
Answer: c
Clarification: As ideal fluid is inviscid, shear stress is zero.

2. Which of the following is not a case of ideal fluid flow?
a) Forced vortex Flow
b) Uniform Flow
c) Sink Flow
d) Superimposed flow
Answer: a
Clarification: Forced vortex Flow does not satisfy the characteristic of ideal fluid flow.

3.What is a special characteristic of uniform flow parallel to X axis?
a) Velocity is constant
b) Acceleration is constant
c) X- component of velocity is constant
d) None of the mentioned
Answer: a
Clarification: Velocity is constant in uniform flow.

4. The source flow is flow coming from a point and moving out in a circular manner.
a) True
b) False
Answer: a
Clarification: The source flow is flow coming from a point and moving out in a radial manner.

5. The sink flow is flow in which fluid moves radially inwards towards a point where it disappears at a variable rate.
a) True
b) False
Answer: b
Clarification: The sink flow is flow in which fluid moves radially inwards towards a point where it disappears at a constant rate.

6. The pattern for streamlines and equipotential lines is different for source and sink flow.
a) True
b) False
Answer: b
Clarification: The pattern for streamlines and equipotential lines is different for source and sink flow.

7. In free vortex flow, the flow is linear in nature.
a) True
b) False
Answer: b
Clarification: In free vortex flow, the flow is circular in nature.

8. What is the nature of streamlines of free vortex flow?
a) Concentric
b) Non-concentric
c) Linear
d) None of the mentioned
Answer: a
Clarification: The nature of streamlines of free vortex flow is concentric.

9. For source flow, the radial velocity increases as we move radially outward.
a) True
b) False
Answer: b
Clarification: There is an inverse relation between velocity and radial distance for source flow.

10. When is air assumed to be incompressible?
a) At low speed
b) At high speed
c) Independent of its speed
d) None of the mentioned
Answer: a
Clarification: Air is assumed to be incompressible at low speed.

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250+ TOP MCQs on Kinetic Energy Correction and Momentum Correction Factors and Answers

Fluid Mechanics Multiple Choice Questions on “Kinetic Energy Correction and Momentum Correction Factors”.

1. What is the value of kinetic energy factor during a laminar flow?
a) 1
b) 2
c) 3
d) 4
Answer: b
Clarification: Kinetic energy factor for a fully developed laminar flow is around 2. Laminar flow occurs when a fluid flows in parallel layers. The flow must not have any sort of disruption between the layers of fluid. The fluid flows without a lateral mixing which makes it slide past one another.

2. Which among the following is not an application of the Bernoulli?
a) Sailing
b) Flow through a venture tube
c) Flow through a sharp-edged orifice.
d) Closing of tap water
Answer: b
Clarification: This is mainly because, Bernoulli’s equation is applied only when the fluid is irrotational. It means that the stream lines are not supposed to intersect each other. Also, the equation does not take viscosity into account. Thus, the flow rate decreases when you close the valve.

3. If you double the kinetic energy of an arrow, by what factor does its speed increase?
a) 2
b) 4
c) same
d) √2
Answer: d
Clarification: Kinetic energy depends upon velocity and mass. The relation between K.E with mass and velocity is K.E= 0.5mv2. If we double the kinetic energy, the velocity has to be increased by a factor equal to the square root of two.

4. What is the function of Reynolds number?
a) To detect pressure changes
b) To predict flow patterns
c) Temperature
d) Viscosity
Answer: b
Clarification: Reynolds number is a dimensionless quantity. It is used to predict flow patterns in different types of fluid flow. At lower Reynold’s number, the flow is laminar. At higher Reynolds number, the flow is turbulent.

5. When a bullet hits a solid block and gets embedded into it. What is conserved?
a) Momentum only
b) Kinetic energy only
c) Momentum and kinetic energy
d) Mass
Answer: a
Clarification: When the bullet is released from the gun, it moves through the individual air molecules. These molecules tend to vibrate which cannot be seen though our naked eye. The solid block acts as a “momentum sink”. It’s so big when compared to a tiny bullet that it can absorb all the momentum without visibly moving.

6. If the kinetic energy is increased 4 times its initial value, then how does its momentum change?
a) 100%
b) 50%
c) 200%
d) 150%
Answer: a
Clarification: Kinetic energy depends upon velocity and mass. The relation is K.E= 0.5mv2. If we increase the kinetic energy by 4 times its initial value, the momentum has to be increased by 100% its initial value.

7. When a charged body enters a uniform magnetic field. How will it’s kinetic energy change?
a) Doubles
b) 4 times
c) Constant
d) Triples
Answer: c
Clarification: The kinetic energy remains a constant as the magnetic field always exerts a force perpendicular to the particle’s velocity. So, there is no change in the velocity of the fluid. Therefore, kinetic energy remains the same.

8. What is the relation between kinetic energy and momentum?
a) p=m/v
b) p=mva
c) p=mv
d) p=m
Answer: c
Clarification: Kinetic energy depends upon velocity and mass. The relation is K.E= 0.5mv2. The momentum(p) of the body=mv. Now, equating the two we get, K.E=0.5mv2=p2/2m. Therefore, the relation between kinetic energy and momentum is (p=mv).

9. How can you slow down a fast neutron?
a) Applying an electric field
b) Using shield
c) Elastic collision
d) Heavy water
Answer: d
Clarification: The fast neutrons are converted to thermal neutrons when they are passed through heavy water(D2O). The key factor for the neutrons to slow down are its atomic number. The velocity of the fast neutrons decreases with a few collisions.

10. If a cricket ball moves with a velocity ‘v’ and collides with a tiny table tennis ball. After an elastic collision, at what velocity will the second ball move?
a) v
b) v/2
c) 2v
d) v2
Answer: c
Clarification: Since the collision is elastic, the cricket ball having a higher mass than that of the tiny table tennis ball will hit and generate a higher velocity. After immediate impact, the table tennis ball will move exactly with twice the velocity of the cricket ball.

250+ TOP MCQs on Rayleighs Method and Answers

Fluid Mechanics Multiple Choice Questions on “Rayleighs Method”.

1. What is the mathematical technique used to predict physical parameters?
a) Combustion analysis
b) Pressure analysis
c) Dimensional analysis
d) Temperature analysis
Answer: c
Clarification: Dimensional analysis is a process which is used to determine physical parameters that influence the fluid flow. The analysis is based on the fundamental units. The fundamental units are mass, length and time.

2. Which among the following method is used to find a functional relationship with respect to a parameter?
a) Rayleigh’s method
b) Rutherford’s method
c) Newton’s laws
d) Doppler effect
Answer: a
Clarification: Rayleigh’s method is a basic method for finding the functional relationship. The functional relationship is found with respect to a physical parameter. It is illustrated using the MLT system.

3. Which among the following is not the correct symbol?
a) Size- l
b) Velocity – v
c) Gravity – g
d) Viscosity – a
Answer: d
Clarification: The symbol used for viscosity is false. Viscosity is denoted by the symbol ‘µ’ (Mew). It is defined as the resistance to flow of fluid. Resistance takes place as one layer of fluid slides over the other.

4. Which among the following is the correct format for Rayleigh’s method?
a) D = f(l,ρ,μV,g)
b) D = (l,ρ,μV,g)
c) D = f
d) D = f(lpv)
Answer: a
Clarification: The correct format for Rayleigh’s method is D = f(l,ρ,μV,g). Where, D is the dimensional analysis, ‘f’ is the function, and the variables inside the bracket are the physical parameters to determine the function.

5. What does ‘C’ denote in D = ClaρbμcVdge?
a) Function
b) Dimensions
c) Dimensionless constant
d) Number of parameters
Answer: c
Clarification: ‘C’ in D = ClaρbμcVdge denotes dimensionless constant and a,b,c,d,e, are its exponents. This is the fundamental purpose of Rayleigh’s method.

6. Why does Rayleigh’s method have limitations?
a) To many variables
b) Format
c) Exponents in between variables
d) Many exponents
Answer: c
Clarification: The main limitation of the Rayleigh’s method is that it has exponential relationship between the variables. It makes it more complex for solving. Since, more variables with exponents will lead to a confusion in the solving process.

7. Which among the following is same as the Rayleigh’s method?
a) Buckingham method
b) Dead weight method
c) Conveyor method
d) Ionization method
Answer: a
Clarification: Buckingham method is also called as the ‘pi’ theorem method. This method can be illustrated by various moving components. It plays an important role in finding the drag of various moving objects.

8. Which among the following is not a dimensionless number?
a) Reynolds
b) Froude
c) Mach
d) Cartesian
Answer: d
Clarification: Dimensionless numbers are numbers with a dimension of one. It is a pure number. It does not contain any physical unit. No change takes place due to altering of any variable.

250+ TOP MCQs on Types of Flow in Channels and Answers

Fluid Mechanics Multiple Choice Questions on “Types of Flow in Channels”.

1. The flow characteristics of a channel does not change with time at any point. What type of flow is it?
a) Steady flow
b) Uniform flow
c) Laminar flow
d) Turbulent flow
Answer: a
Clarification: The flow characteristics unchanged with time is a steady flow, characteristics unchanged with space is a uniform flow. Laminar and turbulent flows are classified with reference to Reynolds number.

2. The Reynolds number for a flow in a channel is 1000. What type of flow is it?
a) Laminar
b) Turbulent
c) Transition
d) Steady
Answer: c
Clarification: Reynolds number – 500 to 600 – Laminar flow
Reynolds number – 500 to 2000 – Transition
Reynolds number – > 2000 – Turbulent flow.

3. The ratio of inertia force and gravitational force is called as ______
a) Reynolds number
b) Stokes number
c) Froude’s number
d) Euler’s number
Answer: c
Clarification: Froude’s number is the ratio of inertia forces and gravitational forces. Froude’s number is used to classify the flow into critical, sub critical and super critical.

4. The Froude’s number for a flow in a channel section is 1. What type of flow is it?
a) Sub Critical
b) Critical
c) Super critical
d) Tranquil
Answer: b
Clarification: Froude’s number = 1 – Critical flow
Froude’s number < 1 – Sub Critical flow
Froude’s number > – Super Critical flow.

5. What is the Froude’s number for a channel having mean velocity 4.34 m/s and mean hydraulic depth of 3m?
a) 0.4m
b) 0.6m
c) 0.7m
d) 0.8m
Answer: d
Clarification: Froude’s number (Fr) = V/ (gD2)
= 4.34/ (9.81) (32)
= 0.8m.

6. Calculate the mean hydraulic radius for a channel having 20m2 cross sectional area and 50m of wetted perimeter.
a) 0.4m
b) 0.5m
c) 0.6m
d) 0.7m
Answer: a
Clarification: Hydraulic Radius(R) = A/P
= 20/50
= 0.4m.

7. Calculate the mean hydraulic depth of a channel having top width of 7m and cross sectional area of 35m2.
a) 4m
b) 5m
c) 6m
d) 7m
Answer: b
Clarification: Hydraulic depth (D) = A/T
= 35/7
= 5m.

8. Estimate the section factor for a channel section having cross sectional area of 40m2 and hydraulic depth of 6m.
a) 94.3
b) 95.6
c) 97.9
d) 100
Answer: c
Clarification: Section factor (Z) = A√D
= 40√6
= 97.9.

9. Calculate the Froude’s number for a channel having discharge of 261.03m3/s, cross sectional area of 42m2 and the top width being 6m.
a) 0.65
b) 0.72
c) 0.38
d) 0.75
Answer: d
Clarification: Fr= V⁄√gD
V = Q/A
V = 261.03/42 = 6.215 m/s
D = A/T = 42/6 = 7m
Fr = 0.75 (Subcritical).

10. Calculate the aspect ratio having channel width of 6m and depth of 8m.
a) 0.75m
b) 1.33m
c) 1.50m
d) 1.68m
Answer: b
Clarification: Aspect ratio = Depth / width
= 8/6 = 1.33m.

11. Estimate the type of flow in a channel having cross sectional area of 50m2 and top of the channel is 5m. The mean velocity of flow is 0.1m/s and the absolute viscosity of water is 0.625 N-s/m2.
a) Laminar
b) Turbulent
c) Transition
d) Steady
Answer: c
Clarification: Reynolds number (Re)=1000VD/µ
Re = 1000(0.1) (D)/ 0.625
D = A/T = 50/5 = 10 m
Re = 1000(0.1) (10)/ 0.625
= 1600
Transition flow (500 – 2000).

250+ TOP MCQs on Introduction to Fluid Mechanics and Answers

Fluid Mechanics Multiple Choice Questions on “Introduction to Fluid Mechanics”.

1. Which one is in a state of failure?
a) Solid
b) Liquid
c) Gas
d) Fluid
Answer: d
Clarification: A fluid is a Tresca material with zero cohesion. In simple words, fluid is in a state of failure.

2. A small shear force is applied on an element and then removed. If the element regains it’s original position, what kind of an element can it be?
a) Solid
b) Liquid
c) Fluid
d) Gaseous
Answer: a
Clarification: Fluids (liquids and gases) cannot resist even a small shear force and gets permanently deformed. Hence, the element must be a solid element.

3. In which type of matter, one won’t find a free surface?
a) Solid
b) Liquid
c) Gas
d) Fluid
Answer: c
Clarification: Solid molecules have a definite shape due to large inter-molecular forces. In liquids, molecules are free to move inside the whole mass but rarely escape from itself. Thus, liquids can form free surfaces under the effect of gravity. But, in case of gases, molecules tend to escape due to low forces of attraction. Thus, gases won’t form any free surface.

4. If a person studies about a fluid which is at rest, what will you call his domain of study?
a) Fluid Mechanics
b) Fluid Statics
c) Fluid Kinematics
d) Fluid Dynamics
Answer: b
Clarification: Fluid Mechanics deals with the study of fluid at rest or in motion with or without the consideration of forces, Fluid Statics is the study of fluid at rest, Fluid Kinematics is the study of fluid in motion without consideration of forces and Fluid Dynamics is the study of fluid in motion considering the application forces.

5. The value of the compressibility of an ideal fluid is
a) zero
b) unity
c) infinity
d) more than that of a real fluid
Answer: a
Clarification: Ideal fluids are incompressible which means they will have zero compressibility.

6. The value of the Bulk Modulus of an ideal fluid is
a) zero
b) unity
c) infinity
d) less than that of a real fluid
Answer: c
Clarification: Bulk modulus k is the reciprocal of compressibility fi.
k = 1⁄fi
Ideal fluids are incompressible which means fi = 0. Thus, k will be infinity.

7. The value of the viscosity of an ideal fluid is
a) zero
b) unity
c) infinity
d) more than that of a real fluid
Answer: a
Clarification: Ideal fluids are non-viscous which means they will have zero viscosity.

8. The value of the surface tension of an ideal fluid is
a) zero
b) unity
c) infinity
d) more than that of a real fluid
Answer: a
Clarification: Ideal fluids haze zero surface tension but real fluids have some finite value of surface tension.