300+ REAL TIME Fluid Mechanics Objective Questions & Answers 2023

250+ TOP MCQs on Dimensional Homogenity and Answers

Fluid Mechanics Multiple Choice Questions on “Dimensional Homogenity”.

1. Which among the following is not a fundamental dimension?
a) [L]
b) [M]
c) [T]
d) [kg]
Answer: d
Clarification: It is essential to adopt a consistent dimensional quantity. Thus, we adopt a basic form to categorize dimension quantities. For this purpose, we adopt a comparison of the quantities in SI or MKS units.

2. The fundamental dimensional quantities are related by________
a) Avagadaro’s law
b) Newton’s second law
c) Newtons first law
d) Newton’s third law
Answer: b
Clarification: Newton’s 2^nd law is the most suitable one for determining the dimensional quantities. We know that, F=ma. Where F = Force , m = mass in kg, and a= acceleration in m/s².

3. Force can be written as______
a) [M][L][T]^-2
b) [M][L][T]²
c) [M][L][T]
d) [M][L][T]³
Answer: a
Clarification: Force can be written dimensionally by [F]= [M][L][T]^-2. This is by adopting the basic SI or MKS units. Where, [M] is the mass, [L] is the length and [T] is the time. Thus, the correct option is [M][L][T]^-2.

4. How can we write power using the MLT system?
a) [M][L][T]^-2
b) [M][L]²[T]³
c) [M][L][T]
d) [M][L][T]³
Answer: b
Clarification: Power can be written dimensionally by [M][L]2[T]³. This is by adopting the basic SI or MKS units. Where, [M] is the mass, [L] is the length and [T] is the time. Thus, the correct option is [M][L]²[T]³.

5. How can we write dynamic viscosity using the MLT system?
a) [M][L][T]^-2
b) [M][L]²[T]³
c) [M][L]^-1[T]^-1
d) [M][L][T]³
Answer: c
Clarification: Dynamic viscosity can be written dimensionally by [M][L]-1[T]^-1. This is by adopting the basic SI or MKS units. Where, [M] is the mass, [L] is the length and [T] is the time. Thus, the correct option is [M][L]^-1[T]^-1.

6. How can we write kinematic viscosity using the MLT system?
a) [M][L][T]^-2
b) [M]⁰[L]²[T]^-1
c) [M][L]^-1[T]^-1
d) [M][L][T]³
Answer: b
Clarification: Kinematic viscosity can be written dimensionally by [M]0[L]2[T]^-1. This is by adopting the basic SI or MKS units. Where, [M] is the mass, [L] is the length and [T] is the time. Thus, the correct option is [M]⁰[L]²[T]^-1.

7. How can we write momentum using the MLT system?
a) [M][L][T]^-2
b) [M]⁰[L]²[T]^-1
c) [M][L][T]^-1
d) [M][L][T]³
Answer: c
Clarification: Momentum can be written dimensionally by [M][L][T]^-1. This is by adopting the basic SI or MKS units. Where, [M] is the mass, [L] is the length and [T] is the time. Thus, the correct option is [M][L][T]^-1.

8. How can we write specific weight using the FLT system?
a) [F]
b) [F][T]
c) [F][L][T]
d) [L]
Answer: a
Clarification: Specific can be written dimensionally by [F]. This is by adopting the basic SI or MKS units (FLT system). Where, [F] is the mass, [L] is the length and [T] is the time. Thus, the correct option is [F].

9. How can we write specific mass using the MLT system?
a) [M][L][T]^-2
b) [M]⁰[L]²[T]^-1
c) [M][L]^-3[T]⁰
d) [M][L][T]³
Answer: c
Clarification: Specific mass can be written dimensionally by [M][L]-3[T]⁰. This is by adopting the basic SI or MKS units. Where, [M] is the mass, [L] is the length and [T] is the time. Thus, the correct option is [M][L]^-3[T]⁰.

10. How can we write energy using the MLT system?
a) [M][L]²[T]²
b) [M]⁰[L]²[T]^-1
c) [M][L]^-3[T]⁰
d) [M][L][T]³
Answer: a
Clarification: Energy or work can be written dimensionally by [M][L]2[T]². This is by adopting the basic SI or MKS units. Where, [M] is the mass, [L] is the length and [T] is the time. Thus, the correct option is [M][L]²[T]².

250+ TOP MCQs on Flow of Compressible Fluid through Orifices and Nozzles and Answers

Fluid Mechanics Multiple Choice Questions on “Flow of Compressible Fluid through Orifices and Nozzles”.

1. What is the Mach number at room temperature?
a) 310 m/s
b) 320 m/s
c) 330 m/s
d) 340 m/s
Answer: d
Clarification: Mach number is defined as the ratio of the speed of an object to the speed of sound. Mach number is denoted by ‘M’. Mach number ranges from zero to infinity. It falls into several flow regimes. It is 340 m/s at room temperature.

2. In a one-dimensional flow, the gas flows through one spatial dimension, namely its length.
a) True
b) False
Answer: a
Clarification: One dimensional flow refers to the flow of gas through a duct or channel in which the flow parameters are assumed to change significantly along a particular dimension. In this case, it’s about its duct length.

3. The compressible flow is assumed to be _____________
a) Isentropic
b) Adiabatic
c) Polytropic
d) Isentropic and adiabatic
Answer: a
Clarification: Compressible flow is a branch of fluid mechanics that deals with different types of flow. Its main significance lies on the change in fluid density. It deals with gas dynamics. Flow is assumed to be isentropic.

4. Ratio of duct length to width length in a compressible flow is_______
a) More than 5
b) Less than 5
c) More than or equal to 5
d) Less than or equal to 5
Answer: d
Clarification: In a compressible flow, the flow is usually in a single dimension. One dimensional flow refers to the flow of gas through a duct or channel in which the flow parameters are assumed to change significantly. Thus, it is less than or equal to 5.

5. The fluid speed through the nozzle is altered with________
a) Acceleration
b) Deceleration
c) Constant speed
d) Zero
Answer: a
Clarification: The fluid speed through the nozzle is altered as the speed accelerates from subsonic speed to supersonic speed in a regime. It alters a nozzle and a diffuser.

6. What happens to velocity in the converging duct?
a) Increases
b) Decreases
c) Same
d) Independent
Answer: a
Clarification: Mass flow rate is given by Q = m/p. This is a relation expressed for mass flow rate. With the presence of a converging duct, the velocity increases. At this point, the area of the duct is less than zero.

7. What happens to velocity in the diverging duct?
a) Increases
b) Decreases
c) Same
d) Independent
Answer: b
Clarification: Mass flow rate is given by Q = m/p. This is a relation expressed for mass flow rate. With the presence of a converging duct, the velocity decreases. At this point, the area of the duct is more than zero.

8. The area of the duct is either maximum or minimum when the_________
a) Mach number = 1
b) Mach > 1
c) Mach = 0
d) Mach < 0
Answer: a
Clarification: Mass flow rate is given by Q = m/p. This is a relation expressed for mass flow rate. The area of the duct is either maximum or minimum when the Mach number of the fluid flow is exactly one.

9. Which among the following is an assumption of the compressible flow?
a) Resistance to flow of object
b) No-slip condition
c) Known mass flow rate
d) Resistance to flow of heat
Answer: b
Clarification: The related assumption of a compressible fluid flow is No-slip condition. It is assumed that the flow velocity at the solid surface is equal to the velocity of the surface itself. It is in direct consequence of the continuum flow.

10. Which among the following is an example of a converging-diverging nozzle?
a) De Laval nozzle
b) High velocity nozzle
c) Magnetic nozzle
d) Vacuum nozzle
Answer: a
Clarification: De-Laval nozzle is an example of a converging diverging nozzle. It a tube that is pinched in the mid marking with a particular balance. It is used to accelerate, hot pressurized gases that pass through a higher supersonic speed in the axial thrust.

11. Maximum achievable velocity of a gas is directly proportional to__________
a) Specific heat
b) Deceleration
c) Velocity
d) Pressure
Answer: a
Clarification: Maximum achievable velocity of a gas is directly proportional to the specific heat of gas. It is based on the energy content. It is derived in accordance with the law of conservation of energy.

12. How much pressure ratio makes one Mach number?
a) 0
b) 1
c) 2
d) 3
Answer: c
Clarification: The overall pressure ratio is given by Pb/Pt. The overall pressure ratio must be approximately 2 to attain the Mach number of one. It is because of the changes in the downstream and upstream of flow in the nozzle.

13. Normal shock waves are_______ to the local flow.
a) Parallel
b) Perpendicular
c) Same
d) Independent
Answer: b
Clarification: Normal shock waves are perpendicular to the local flow direction. The shock waves occur when the pressure builds up into an extremely thin shockwave that converts energy into heat. The waves thus take over one another.

14. Oblique shock waves are ______ to the local flow.
a) Parallel
b) Perpendicular
c) Less than 90 degrees
d) Independent
Answer: a
Clarification: Oblique shock waves have an angle less than 90 degrees with respect to its local flow. They are similar to the normal shock waves. When there is any disturbance to the fluid flow at a non-zero angle oblique shock is formed.

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 = Cl^aρ^bμ^cV^dg^e?
a) Function
b) Dimensions
c) Dimensionless constant
d) Number of parameters
Answer: c
Clarification: ‘C’ in D = Cl^aρ^bμ^cV^dg^e 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.