Category: Fluid Mechanics Objective Questions

250+ TOP MCQs on Continuity Equation in Two and Three Dimensions and Answers

Fluid Mechanics Multiple Choice Questions on “Continuity Equation in Two and Three Dimensions”.

1. The continuity equation is based on the premise of-
a) Law of conservation of energy
b) Law of conservation of mass
c) Law of conservation of momentum
d) None of the mentioned
Answer: b
Clarification: Continuity equation is based on the the principle of conservation of mass.

2. The continuity equation is only applicable to incompressible fluid.
a) True
b) False
Answer: b
Clarification: The continuity equation is only applicable to incompressible as well as compressible fluid.

3. For incompressible fluid flow, if area reduces then what is the effect on the velocity.
a) increases
b) decreases
c) first increases then decreases
d) first decreases then increases
Answer: a
Clarification: According to continuity equation,
Area × velocity = constant
Hence, as area decreases velocity increases.

4. For compressible fluid flow in a pipe, having decrease in specific gravity what will be the effect of decrease in diameter?
a) It will cause increase in velocity
b) It will cause decrease in velocity
c) It remains constant
d) None of the mentioned
Answer: a
Clarification: According to continuity equation,
ρ*A*v = constant
Hence, as density and area decreases velocity is bound to increase.

5. What is the most common assumption while dealing with fluid flow problems using continuity equation?
a) Flow is assumed to be compressible
b) Flow is assumed to be unsteady
c) Flow is assumed to be steady
d) Flow is assumed to be turbulent
Answer: c
Clarification: In majority of the fluid flow problems, flow is assumed to be steady.

6. The diameters of a pipe at the sections 1 and 2 are 8 cm and 13 cm respectively. Find the discharge through pipe if the velocity of water flowing through the pipe at section 1 is 6 m/s. Determine also the velocity at section 2.
a) 2.27 m/s
b) 4.54 m/s
c) 1.13 m/s
d) 3.25 m/s
Answer: a
Clarification: According to continuity equation,
Area × velocity = constant
Area1*Velocity1 = Area2*Velocity2
Velocity2=(Area1*Velocity1)/Area2
= (82 * 6) / 132=2.27 m/s.

7. The continuity equation can only be used for analysis of conserved quantity.
a) True
b) False
Answer: a
Clarification: Continuity equation is defined on a control volume and hence, is applicable only to Conserved quantities.

8. The diameter of a pipe at the section 1 is 9 cm. If the velocity of water flowing through the pipe at section 1 is 4.8 m/s and section 2 is 9 m/s, Determine the area at section 2.
a) 33.93 m2
b) 67.86 m2
c) 16.96 m2
d) 38.66 m2
Answer: a
Clarification: According to continuity equation,
Area × velocity = constant
Area1*Velocity1 = Area2*Velocity2
(Area1*Velocity1)/Velocity2=Area2
Area 2= 33.93 m2.

9. For a flow to be physically possible it must primarily satisfy which equation?
a) Equation of conservation of energy
b) Equation of conservation of mass or continuity equation
c) Equation of conservation of momentum
d) None of the mentioned
Answer: a
Clarification: Fluid flow must satisfy equation of conservation of mass or continuity equation, for itto be physically possible.

10. Continuity equation can also be derived for polar coordinate system
a) True
b) False
Answer: a
Clarification: Continuity equation in polar coordinate is also used for analysis.

250+ TOP MCQs on Shear Stress and Pressure Gradient and Answers

Fluid Mechanics Multiple Choice Questions on “Shear Stress and Pressure Gradient”.

1. What is the unit of shear stress?
a) N/m3
b) N/mm3
c) N/m
d) Pascal
Answer: d
Clarification: Shear stress is defined as the force acting per unit area. Thus, the unit of shear stress is equal to N/m2. Since, 1 Pa =1 N/m2, Pascal is the most suitable one.

2. Shear stress is caused due to _______
a) Friction
b) Temperature
c) Pressure
d) Volume
Answer: a
Clarification: Shear stress is caused due to friction between fluid particles. It is formed due to the presence of fluid viscosity. Shear stress arises from the force vector component which is parallel to the cross section.

3. Which among the following is a formula for shear stress?
a) τ = F*A
b) τ = F/A
c) τ = F/m
d) τ = F*m
Answer: b
Clarification: Shear stress is defined as the force acting per unit area. Shear stresses arise from shear components(forces), which are pairs of equal and opposite forces. These forces act on the opposite side of the object.

4. Which among the following is the correct formula to find out the shear modulus(G)?
a) E/2
b) v/2
c) E/2(1+v)
d) 2E(1+v)
Answer: c
Clarification: Shear modulus is also called as modulus of rigidity. It is defined as the ratio of shear stress to shear strain. Since Young modulus is equal to stress by strain. The most suitable option is option c. (E= Young’s Modulus, v= poison’s ratio)

5. Which among the following is an assumption of Hagen-Poiseuille equation?
a) Fluid is compressible
b) Fluid is uniform
c) Fluid is laminar
d) Fluid is turbulent
Answer: c
Clarification: Fluid flow is laminar as it is assumed to be incompressible and Newtonian. The flow is laminar through the pipe of constant cross section. Thus, there is no acceleration of fluid in the pipe. Therefore, Hagen-Poiseuille assumed that fluid flow is laminar.

6. What is the unit of pressure gradient?
a) Pa/m
b) Nm
c) Pa
d) N/m
Answer: a
Clarification: Pressure gradient is a dimensional quantity. It is expressed in units of pressure per unit length. It determines which quantity and which direction the pressure changes around a particular location.

7. Which of the following is not a basic type of stress?
a) Volumetric stress
b) Shear stress
c) Compressive stress
d) Tensile stress
Answer: a
Clarification: Volumetric stress is not a basic classification among the type of stresses as it describes the tendency of an object to deform in all directions. It deforms when the load acts uniformly in all directions.

8. What type of force does a stress produce?
a) Radial force
b) External force
c) Internal resistive force
d) Axial force
Answer: c
Clarification: According to the continuum mechanics, stress is a physical quantity that produces internal forces. For example: When a solid bar supports a weight, each particle of the bar pushes the particles immediately below it. This happens due to the internal resistive force that is developed due to the stress on the body.

9. Hooke’s law is applicable within what limit?
a) Fracture point
b) Elastic limit
c) Ultimate strength
d) Plastic limit
Answer: b
Clarification: Hooke’s law states that force is directly proportional to its extension. Hooke’s law is applicable within the elastic limit, when the body is deformed. Example: plucking the strings of a guitar.

10. Define Factor of safety
a) Ultimate stress/Permissible stress
b) Ultimate stress/ Shear stress
c) Compressive stress/ Ultimate stress
d) Tensile stress/Shear stress
Answer: a
Clarification: Factor of safety determines the maximum load carrying capacity. It tells us how much stronger the system is than it usually needs to be for a particular specified load. It is the ratio of allowable stress to the actual stress.

250+ TOP MCQs on Maximum Speed of a Reciprocating Pump and Answers

Fluid Mechanics Multiple Choice Questions on “Maximum Speed of a Reciprocating Pump”.

1. A reciprocating pump is a class of _________
a) Negative displacement
b) Positive displacement
c) Zero displacement
d) Infinite displacement
Answer: b
Clarification: A reciprocating pump consists of a piston pump, plunger and diaphragm pump. It is a class of positive displacement. Reciprocating pumps will last for years and decades.

2. The simplest application of the reciprocating pump is___________
a) Piston pump
b) Plunger
c) Diaphragm pump
d) Bicycle pump
Answer: d
Clarification: Bicycle is the pump is the simplest application of the reciprocating pump. It works on the principle of simple hand operated reciprocating pump. It is used to inflate bicycle tires and various sporting balls.

3. Power operated deep well reciprocating pump is divided into__________
a) Single and double acting
b) Single and multi-stage
c) Piston and plunger
d) Conductive and nonconductive
Answer: a
Clarification: Power operated deep well reciprocating pump is divided into single and double acting. It is classified on the basis of its mechanism. It is distinguished depending on the function of the piston.

4. Which among the following is not an example of a reciprocating pump?
a) Hand pump
b) Wind mill
c) Axial piston pump
d) Turbine blades
Answer: d
Clarification: A reciprocating pump is a class of a positive displacement pump. It includes a piston pump, plunger and a diaphragm pump. It has a long life. Turbine blades are not an example of the reciprocating pump.

5. Pump converts mechanical energy into ________
a) Pressure energy only
b) Kinetic energy only
c) Pressure and kinetic energy
d) Potential energy
Answer: c
Clarification: The main function of the pump is to transfer and convert mechanical energy of a motor into pressure energy and kinetic energy. It plays an important role in the transfer of fluid across the pipeline.

6. Which among the following is not a positive displacement pump?
a) Centrifugal
b) Reciprocating
c) Rotary
d) Ionization pump
Answer: a
Clarification: Centrifugal pumps are not a positive displacement pump. They are a subclass dynamic work absorbing turbo machinery. They are used to transport fluids. It transports fluid by conversion of rotational kinetic energy to hydrodynamic kinetic energy.

7. How do we measure the flow rate of liquid?
a) Coriolis method
b) Dead weight method
c) Conveyor method
d) Ionization method
Answer: a
Clarification: Coriolis concept of measurement of fluid takes place through the rotation with the reference frame. It is an application of the Newton’s Law. The device continuously records, regulates and feeds large volume of bulk materials.

8. Which among the following is called as the velocity pump?
a) Centrifugal
b) Reciprocating
c) Rotary
d) Ionization pump
Answer: a
Clarification: Centrifugal pumps are not a positive displacement pump. They are a subclass dynamic work absorbing turbo machinery. They are used to transport fluids. It transports fluid by conversion of rotational kinetic energy to hydrodynamic kinetic energy.

9. Discharge capacity of a reciprocating pump is lower than that of reciprocating pump.
a) True
b) False
Answer: True
Clarification: Discharge capacity of the reciprocating pump is lower than that of the reciprocating pump. Discharge capacity of fluids is defined as the discharge in terms of the volumetric flow rate. It helps to regulate the flow through a cross sectional area.

10. Which among the following is a high-pressure pump?
a) Centrifugal
b) Reciprocating
c) Rotary
d) Ionization pump
Answer: b
Clarification: Reciprocating pump is the most suitable high-pressure pumps at moderate or low discharges. A reciprocating pump is a class of a positive displacement pump. It includes a piston pump, plunger and a diaphragm pump.

250+ TOP MCQs on Area Velocity Relationship for Compressible Flow and Answers

Fluid Mechanics Multiple Choice Questions on “Area Velocity Relationship for Compressible Flow”.

1. The exit velocity in the nozzle increases as per __________
a) Stagnation point
b) Continuity equation
c) Prandtl Number
d) Newton’s law
Answer: b
Clarification: In the nozzle, the exit velocity of the fluid increases as per the continuity equation. Continuity equation is given as Av= constant as per the Bernoulli’s equation. It is essential for an incompressible flow.

2. With the increase in pressure, the exit velocity _________
a) Decreases
b) Increases
c) Same
d) Independent
Answer: a
Clarification: Pressure is inversely proportional to the velocity. So, with the increase in pressure, the exit velocity decreases. We know that the pressure is equal to force per unit area, this contradicts the above statement.

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. Pumps increase __________
a) Pressure
b) Velocity
c) Momentum
d) Heat
Answer: a
Clarification: Pumps increase pressure rather than velocity. During the pumping process, a housing is provided for the pumping elements. These parts can change the speed. Pumps create a passage way that will squirt the fluid passing through it. Thus, pumping increases pressure.

5. Which among the following is the formula for volumetric flow rate?
a) Q = v/A
b) Q = Av
c) Q = A+v
d) Q = A-v
Answer: b
Clarification: Volumetric flow rate is given by Q= A.v. Where v is the flow velocity of the fluid, and A is the area of cross section of the surface. Area of a surface is also called as the vector area. Thus, the right answer is Q = Av.

6. Which among the following is the formula for mass flow rate?
a) Q = m/p
b) Q = mp
c) Q = m + p
d) Q = m – p
Answer: b
Clarification: Mass flow rate is given by Q=m/p. This is a relation expressed for mass flow rate. When ‘m’ is the mass flow rate. And, p is the density of the fluid flow. They are expressed in their standard units.

7. Compressible flow is a flow that deals with ______
a) Fluid temperature
b) Fluid pressure
c) Fluid density
d) Fluid geometry
Answer: c
Clarification: Compressible flow is a branch of fluid mechanics that deals with different types of flow. Its main significance lies in the change in fluid density. Thus, the correct option is Fluid density .

8. Compressible flow mainly deals with _______
a) Solid dynamics
b) Liquid dynamics
c) Gas dynamics
d) Solid and liquid dynamics
Answer: c
Clarification: Compressible flow is a branch of fluid mechanics that deals with different types of flow. Its main significance lies in the change in fluid density. It deals with gas dynamics.

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 with the continuum flow.

10. What is Mach number?
a) Speed of object * speed of sound
b) Speed of object /speed of sound
c) Speed of object + speed of sound
d) Speed of object- speed of sound
Answer: b
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.

250+ TOP MCQs on Fluid Pressure at a Point and Pascal’s Law and Answers

Fluid Mechanics Interview Questions and Answers for Experienced people on “Fluid Pressure at a Point & Pascal’s Law”.

1. A Hydraulic press has a ram of 30 cm diameter and a plunger of of 2 cm diameter. It is used for lifting a weight of 35 kN. Find the force required at the plunger.
a) 233.3 kN
b) 311.1 kN
c) 466.6 kN
d) 155.5 kN
Answer: d
Clarification: F/a=W/A
F=(35000*3.142*.02*.02)/(3.142*0.3*0.3)
=155.5 kN.

2. The pressure at a point in the fluid is 4.9 N/cm2. Find height when the fluid under consideration is in oil of specific gravity of 0.85.
a) 5.83 m
b) 11.66 m
c) 17.49 m
d) 8.74 m
Answer: a
Clarification: Height=p/ρg
=48620/850*9.81
=5.83 m.

3. An open tank contains water upto a depth of 350 cm and above it an oil of specific gravity 0.65 for a depth of 2.5 m. Find the pressure intensity at the extreme bottom of the tank.
a) 5.027 N/cm2
b) 10.05 N/cm2
c) 2.51 N/cm2
d) None of the mentioned
Answer: a
Clarification: p= (specific gravity of water* height of water + specific gravity of oil* height of oil) * 9.81
= 5.027 N/cm2.

4. The diameters of a small piston and a large piston of a hydraulic jack are 45 mm and 100 mm respectively.Force of 0.09 kN applied on smaller in size piston. Find load lifted by piston if smaller in size piston is 40 cm above the large piston. The density of fluid is 850 kg/m3
a) 60 N/cm2
b) 12 N/cm2
c) 30 N/cm2
d) None of the mentioned
Answer: a
Clarification: Pressure at bottom of tank =ρgh + F/a
=850*9.81*0.4 + 90/3.142*0.045*0.045
=60 N/cm2.

5. If fluid is at rest in a container of a narrow mouth at a certain column height and same fluid is at rest at same column height in a container having broad mouth, will the pressure be different at certain depth from fluid surface.
a) Pressure will be same for both.
b) Pressure will be more for narrower mouth
c) Pressure will be less for narrower mouth
d) None of the mentioned
Answer: a
Clarification: As per hydrostatic law, the pressure depends only on the height of water column and not its shape.

6. We can draw Mohr’s circle for a fluid at rest.
a) True
b) false
Answer: b
Clarification: Mohr’s circle is used to denote shear stress distribution. For fluid at rest, there is no shear stress. Hence, we cannot draw Mohr’s circle for fluid at rest.

7. Pressure intensity or force due to pressure gradient for fluid at rest is considered as which kind of force?
a) Surface force
b) Body force
c) Force due to motion
d) None of the mentioned
Answer: a
Clarification: Pressure force is surface force.

8. Calculate the hydrostatic pressure for water moving with constant velocity at a depth of 5 m from the surface.
a) 49 kN/m2
b) 98 kN/m2
c) since fluid is in motion, we cannot analyse
d) None of the mentioned
Answer: a
Clarification: If fluid is moving with uniform velocity we treat it analytically same as if fluid is at rest
p= ρgh.

9. Pressure distribution for fluid at rest takes into consideration pressure due to viscous force.
a) True
b) False
Answer: b
Clarification: Viscous force term in pressure expression for fluid at rest is absent as their is no motion of liquid.

10. Barometer uses the principle of fluid at rest or pressure gradient for its pressure calculation.
a) True
b) False
Answer: a
Clarification: Principle of Barometer is Hydrostatic law.

To practice all areas of Fluid Mechanics for Interviews,

250+ TOP MCQs on Velocity and Acceleration and Answers

Fluid Mechanics Multiple Choice Questions on “Velocity and Acceleration”.

1. The velocity vector in a fluid is given V=5x4+3y2+2z( in metre/sec). What is the acceleration of it at point (1,3,4) ?
a) 40 m/s2
b) 20 m/s2
c) 60 m/s2
d) 80 m/s2
Answer: a
Clarification: By differentiating V=5x4+3y2+2z, the acceleration obtained is V=20x3+6y+2.
on putting the coordinates, the acceleration obtained is 40 m/s2.

2. Determine the third velocity component such that continuity equation is satisfied if two components are u=2y2, w=2xyz.
a) -2xy+x2y+f(y,z)
b) 4xy-x2y+f(y,z)
c) -4xy-x2y+f(y,z)
d) -2xy-x2y+f(y,z)
Answer: c
Clarification: The continuity equation for incompressible is du/dx+dv/dy+dw/dz = 0.
Here du/dx=0 and w=2xy.
On solving by integrating, we get v = -4xy-x2y+f(y,z).

3. Determine the third velocity component such that continuity equation is satisfied if two components are u=x2+y2+z2, v=xy2 – yz2 + xy
a) -3xz-2xyz+z2/3+f(y,z)
b) -3xz+2xyz+z3/3+f(y,z)
c) -3xz-2xyz+z3/3+f(x,z)
d) -3xz-2xyz+z3/3+f(y,z)
Answer: d
Clarification: The continuity equation for incompressible is du/dx+dv/dy+dw/dz = 0.
Here du/dx=2x and v=2xy-z2
On solving by integrating, we get w = -3xz-2xyz+z3/3+f(y,z),

4. A fluid flow field is given by
V=x2yi+y2z-(2xyz+yz)k
Calculate it’s acceleration at the point (1,3,5)
a) 28i-3j+125k
b) 28i-3j-125k
c) 28i+3j+125k
d) None of the mentioned
Answer: d
Clarification: First we have to check whether it satisfies the continuity equation,
The continuity equation for incompressible is du/dx+dv/dy+dw/dz = 0.
(here d/dx, d/dy, d/z represent partial derivative)
The given equation doesn’t satisfy the continuity equation.

5. A fluid flow field is given by
V=y2xi+z2x-(2xyz+yz)k
Calculate it’s acceleration at the point (2,4,4)
a) 36i-27j+100k
b) 36i-27j-100k
c) 28i+27j+100k
d) 36ne of the mentioned
Answer: d
Clarification: First we have to check whether it satisfies the continuity equation,
The continuity equation for incompressible is du/dx+dv/dy+dw/dz = 0.
(here d/dx, d/dy, d/z represent partial derivative)
The given equation doesn’t satisfy the continuity equation.

6. Convective acceleration cannot be found if the fluid flow equation is not satisfying
the continuity equation but local acceleration can be found.
a) True
b) False
Answer: b
Clarification: Convective acceleration and local acceleration cannot be found if the fluid flow equation is not satisfying the continuity equation.

7. Local acceleration has constant value for a steady flow.
a) True
b) False
Answer: b
Clarification: Local acceleration is zero for a steady flow.

8. Total acceleration has the same value as convective acceleration in case of unsteady flow.
a) True
b) False
Answer: b
Clarification: Total acceleration has the same value as convective acceleration in case of steady flow as local acceleration value becomes zero.

9. Which equation must be perfunctorily satisfied while dealing with fluid flow problems?
a) Newton’s second law
b) Newton’s third law
c) Law of conservation of momentum
d) Continuity equation
Answer: d
Clarification: Continuity equation must be perfunctorily satisfied while dealing with fluid flow problems.

10. Convective acceleration is defined as the rate of change of velocity due to change of velocity with respect to time.
a) True
b) False
Answer: b
Clarification: Convective acceleration is defined as the rate of change of velocity due to change of position of fluid particles.