Multiple Choice Questions with answers - Fluid Dynamics

1) Shear stress in static fluid is
a. always zero
b. always maximum
c. between zero to maximum
d. unpredictable
ANSWER: always zero
2) Which branch of fluid mechanics deals with translation, rotation and deformation of
the fluid element without considering the force and energy causing such motion is called as
a. fluid dynamics
b. fluid kinematics
c. fluid kinetics
d. hydraulics
ANSWER: fluid kinematics
3) Inter molecular cohesive force in the fluids is
a. less than that of the solids
b. more than that of the solids
c. equal to that of the solids
d. unpredictable
ANSWER: less than that of the solids
4) The specific weight of the fluid depends upon
a. gravitational acceleration
b. mass density of the fluid
c. both a. and b.
d. none of the above
ANSWER: both a. and b.
5) Which property of the fluid offers resistance to deformation under the action of shear
force?
a. density
b. viscosity
c. permeability
d. specific gravity
ANSWER: viscosity
6) In which method of describing fluid motion, the observer remains stationary and
observes changes in the fluid parameters at a particular point only?
a. Lagrangian method
b. Eulerian method
c. Stationary method
d. All of the above
ANSWER: Eulerian method
7) The rate of increase of velocity with respect to change in the position of fluid particle in
a flow field is called as
a. local acceleration
b. temporal acceleration
c. convective acceleration
d. all of the above
ANSWER: convective acceleration
8) The actual path followed by a fluid particle as it moves during a period of time, is called
as
a. path line
b. streak line
c. filament line
d. stream line
ANSWER: path line
9) The imaginary line drawn in the fluid in such a way that the tangent to any point gives
the direction of motion at the point, is called as
a. path line
b. streak line
c. filament line
d. stream line
ANSWER: stream line
10) Which type of fluid flow is shown in below diagram?













a. Circular flow
b. Rotational flow
c. Irrotational flow
d. None of the above
ANSWER: Irrotational flow
11) The study of force which produces motion in a fluid is called as
a. fluid statics
b. fluid dynamics
c. fluid kinematics
d. none of the above
ANSWER: fluid dynamics
12) Which of the following forces generally act on fluid while considering fluid dynamics?
1. Viscous force
2. Pressure force
3. Gravity force
4. Turbulent force
5. Compressibility force
a. (1), (3), (4) and (5)
b. (1), (2), (3) and (5)
c. (1), (2), (3) and (4)
d. (1), (2), (3), (4) and (5)
ANSWER: (1), (2), (3), (4) and (5)
13) The net force of an ideal flow is equal to the sum of nonzero values of
a. pressure force and gravity force
b. viscous force and gravity force
c. pressure force and viscous force
d. pressure force, viscous force and compressibility force
ANSWER: pressure force and gravity force
14) When the net force acting on a fluid is the sum of only gravity force, pressure force
and viscous force, the equation is called as
a. Reynold's equation of motion
b. Navier-stockes equation of motion
c. Euler's equation of motion
d. none of the above
ANSWER: Navier-stockes equation of motion
15) In a steady, ideal flow of an incompressible fluid, total energy at any point of the fluid
is always constant. This theorem is known as
a. Euler's theorem
b. Navier-stockes theorem
c. Reynold's theorem
d. Bernoulli's theorem
ANSWER: Bernoulli's theorem
16) The flow of fluid will be laminar when,
a. Reynold's number is less than 2000
b. the density of the fluid is low
c. both a. and b.
d. none of the above
ANSWER: both a. and b.
17) How should be the viscosity of the flowing fluid for laminar flow?
a. viscosity of the fluid should be as low as possible, for laminar flow
b. viscosity of the fluid should be as high as possible, for laminar flow
c. change in viscosity of the flowing fluid does not affect its flow
d. unpredictable
ANSWER: viscosity of the fluid should be as high as possible, for laminar flow
18) Below diagram shows the velocity distribution of fluid flow through a pipe. Flow is
laminar.
What is the ratio of maximum velocity to average velocity?

a. 1
b. 2
c. 4
d. 3.14
ANSWER: 2
19) Coefficient of friction for laminar flow is given as
Where,
Re = Reynold's number
a. (Re / 32)
b. (32 / Re)
c. (Re / 16)
d. (16 / Re)
ANSWER: (16 / Re)
20) What is the ratio of maximum velocity to average velocity, when the fluid is passing
through two parallel plates and flow is laminar?
a. 3/2
b. 2/3
c. 4/3
d. 3/4
ANSWER: 3/4
21) The head loss through fluid flowing pipe due to friction is
a. the minor loss
b. the major loss
c. both a. and b.
d. none of the above
ANSWER: the major loss
22) What is Darcy-Weisbach formula for heat loss due to friction?
Where,
f = Darcy's coefficient of friction
a. hf = (f l V2) / (g d)
b. hf = (f l V2) / (2 g d)
c. hf = (4 f l V2) / (2 g d)
d. hf = (16 f l V2) / (2 g d)
ANSWER: hf = (4 f l V2) / (2 g d)
23) Minor losses occur due to
a. sudden enlargement in pipe
b. sudden contraction in pipe
c. bends in pipe
d. all of the above
ANSWER: all of the above
24) Minor losses do not make any serious effect in
a. short pipes
b. long pipes
c. both the short as well as long pipes
d. cannot say
ANSWER: long pipes
25) What is the correct formula for loss at the exit of a pipe?
a. hL = 0.5 (V2 / 2g)
b. hL = (V2 / 2g)
c. hL = (2 V2 / g)
d. hL = (4 V2 / g)
ANSWER: hL = (V2 / 2g)

Mechanical Engineering Important MCQ (Qustions on Fluid Dynamics)

1) Shear stress in a turbulent flow is given by the formula
τ = η (du / dy)
Where η (eta) is,
a. eddy viscosity
b. apparent viscosity
c. virtual viscosity
d. all of the above
ANSWER: all of the above
2) Magnitude of eddy viscosity for laminar flow is
a. less than zero
b. zero
c. greater than zero
d. unpredictable
ANSWER: zero
3) Kinematic eddy viscosity (ε) is the ratio of
a. eddy viscosity (η) to dynamic viscosity (μ)
b. eddy viscosity (η) to kinematic viscosity (ν)
c. kinematic viscosity to eddy viscosity (η)
d. eddy viscosity (η) to mass density (ρ)
ANSWER: eddy viscosity (η) to mass density (ρ)
4) Friction factor for laminar flow is given by
a. (Re /64)
b. (64 / Re)
c. (Re / 16)
d. (16 / Re)
ANSWER: (64 / Re)
5) What is temporal mean velocity?
a. The average of velocities at a point over a certain period of time
b. The average of velocities of a single particle over different locations in a fluid flow
c. None of the abov
ANSWER: The average of velocities at a point over a certain period of time
6) The friction factor in fluid flowing through pipe depends upon
a. Reynold's number
b. relative roughness of pipe surface
c. both a. and b.
d. none of the above
ANSWER: both a. and b.
7) What is the effect of change in Reynold's number on friction factor in turbulent flow?
a. As the Reynold's number increases the friction factor increases in turbulent flow
b. As the Reynold's number increases the friction factor decreases in turbulent flow
c. change in Reynold's number does not affect the friction factor in turbulent flow
d. unpredictable
ANSWER: As the Reynold's number increases the friction factor decreases in turbulent
flow
8) What is the formula for determining the size of equivalent pipe for two pipes of lengths
L1, L2 and diameters d1, d2 respectively?
Where,
L = L1 + L2
a. (L / d) = (L1 / d1) + (L2 / d2)
b. (L / d2 ) = (L1 / d1
2) + (L2 / d2
2)
c. (L / d3) = (L1 / d1
3 ) + (L2 / d2
3)
d. (L / d5) = (L1 / d1
5 ) + (L2 / d2
5)
ANSWER: (L / d5) = (L1 / d1
5 ) + (L2 / d2
5)
9) What is a syphon?
a. A long bend pipe used to carry water from a reservoir at a higher level to another reservoir at a
lower level when two reservoirs are separated by a hill
b. A long bend pipe used to carry water from a reservoir at a lower level to another reservoir at a
higher level with some work input when two reservoirs are separated by a hill
c. A long bend pipe used to carry water from one reservoir to another reservoir when two
reservoirs are at same elevation
d. Unpredictable
ANSWER: A long bend pipe used to carry water from a reservoir at a higher level to
another reservoir at a lower level when two reservoirs are separated by a hill
10) The highest point of syphon is called as
a. syphon top
b. summit
c. reservoir
d. none of the above
ANSWER: summit
11) Match the following physical quantities in Group 1 with their dimensions in Group 2.
1. Work done (Energy) (W) ----------------------------- A. [M L 2 T – 3 ]
2. Power (P) ------------------------------------------------ B. [M L – 1 T – 1 ]
3. Momentum (M) ---------------------------------------- C. [M L 2 T – 2 ]
4. Modulus of elasticity (E) ----------------------------- D. [M L T – 1 ]
5. Dynamic viscosity (μ) --------------------------------- E. [M L – 1 T – 2 ]
a. 1-(C), 2-(A), 3-(D), 4-(E), 5-(B)
b. 1-(A), 2-(C), 3-(D), 4-(E), 5-(B)
c. 1-(C), 2-(A), 3-(E), 4-(B), 5-(D)
d. 1-(D), 2-(E), 3-(B), 4-(A), 5-(C)
ANSWER: 1-(C), 2-(A), 3-(D), 4-(E), 5-(B)
12) Which of the following equations is not dimensionally homogeneous?
Consider standard symbols for quantities.
a. (Force) F = m x a
b. (Head Loss due to friction) hf = (f L V2) / (2 g d)
c. (Torque) T = F x Distance
d. None of the above
ANSWER: None of the above
13) Which of the following is a dimensionless equation?
a. Reynold's equation
b. Euler's equation
c. Weber's equation
d. All of the above
ANSWER: All of the above
14) Which of the following number is applicable in open hydraulic structure such as
spillways, where gravitational force is predominant?
a. Reynold's Number
b. Euler's Number
c. Weber's Number
d. Froude's Number
ANSWER: Froude's Number
15) Square root of the ratio of inertia force to elastic force is called as
a. Mach's Number
b. Cauchy's Number
c. Both a. and b.
d. None of the above
ANSWER: Both a. and b.
16) Boundary layer thickness is the distance from the boundary to the point where
velocity of the fluid is
a. equal to 10% of free stream velocity
b. equal to 50% of free stream velocity
c. equal to 90% of free stream velocity
d. equal to 99% of free stream velocity
ANSWER: equal to 99% of free stream velocity
17) The component of the total force exerted by fluid on a body in the direction parallel to
the direction of motion is called as
a. lift
b. drag
c. both a. and b.
d. none of the above
ANSWER: drag
18) The sum of components of shear forces in the direction of flow of fluid is called as
a. shear drag
b. friction drag
c. skin drag
d. all of the above
ANSWER: all of the above
19) The body whose surface does not coincide with the streamline when places in a flow is
called as
a. streamline body
b. wave body
c. bluff body
d. induced body
ANSWER: bluff body
20) Which type of body is an airfoil?
a. streamline body
b. wave body
c. bluff body
d. induced body
ANSWER: streamline body
21) Bulk modulus is the ratio of
a. shear stress to volumetric strain
b. volumetric strain to shear stress
c. compressive stress to volumetric strain
d. volumetric strain to compressive stress
ANSWER: compressive stress to volumetric strain
22) When is a liquid said to be not in a boiling or vaporized state?
a. If the pressure on liquid is equal to its vapour pressure
b. If the pressure on liquid is less than its vapour pressure
c. If the pressure on liquid is more than its vapour pressure
d. Unpredictable
ANSWER: If the pressure on liquid is more than its vapour pressure
23) One litre of a certain fluid weighs 8N. What is its specific volume?
a. 2.03 x 10– 3 m3/kg
b. 20.3 x 10– 3 m3/kg
c. 12.3 x 10– 3 m3/kg
d. 1.23 x 10– 3 m3/kg
ANSWER: 1.23 x 10– 3 m3/kg
24) What is the correct formula for absolute pressure?
a. Pabs = Patm – Pgauge
b. Pabs = Pvacuum – Patm
c. Pabs = Pvacuum + Patm
d. Pabs = Patm+ Pgauge
ANSWER: Pabs = Patm+ Pgauge
25) According to Archimede's principle, if a body is immersed partially or fully in a fluid
then the buoyancy force is _______ the weight of fluid displaced by the body.
a. equal to
b. less than
c. more than
d. unpredictable
ANSWER: equal to

Questions on Fluid Mechanics (Mechanical Engineering Important MCQ)

1) Which of the following statements are true for dimensional analysis?
1. The functional relationship between dependent and non-dependent variables can be
expressed into dimensionless terms by dimensional analysis
2. In model testing, it reduces the number of variables into three numbers
3. It is used to change the theoretical equation into dimensionless form
4. It helps to convert the units of quantities from one system to another system
a. (1), (2) and (3)
b. (2), (3) and (4)
c. (1), (3) and (4)
d. (1), (2), (3) and (4)
ANSWER: (1), (2), (3) and (4)
2) The unit of physical quantity which does not depend on the unit of any other physical
quantity is called as
a. independent dimension
b. fundamental dimension
c. core dimension
d. none of the above
ANSWER: fundamental dimension
3) Which of the following is not a primary quantity?
a. Mass (M)
b. Temperature (θ)
c. Time (T)
d. None of the above
ANSWER: None of the above

4) What are the dimensions of force?
a. [M L T – 2 ]
b. [M L T – 1 ]
c. [M L 2 T – 2 ]
d. [M L 2 T 2 ]
ANSWER: [M L T – 2 ]
5) Which of the following quantities has the dimensions [M0 L0 T 0]
a. Density
b. Stress
c. Strain
d. Strain Rate
ANSWER: Strain
6) How is the intensity of shear stresses over the boundary layer?
a. small
b. large
c. sometimes small and sometimes large
d. cannot say
ANSWER: large
7) The velocity gradients over the boundary layer are
a. small
b. large
c. sometimes small and sometimes large
d. cannot say
ANSWER: large
8) What is the effect of free stream velocity on thickness of boundary layer?
a. Increase in free stream velocity increases the boundary layer thickness
b. Increase in free stream velocity decreases the boundary layer thickness
c. The boundary layer thickness does not get affected by any change in free stream velocity
d. unpredictable
ANSWER: Increase in free stream velocity decreases the boundary layer thickness
9) If viscosity of fluid is more, the thickness of boundary layer is
a. more
b. less
c. not affected by change in viscosity
d. unpredictable
ANSWER: more
10) The region in the turbulent boundary layer zone, adjacent to the solid surface of the
plate is called as
a. laminar sub layer
b. turbulent sub layer
c. solid sub layer
d. solid layer
ANSWER: laminar sub layer
11) Newton's law of viscosity states that
a. the shear stress applied to the fluid is directly proportional to the velocity gradient (du/dy)
b. the shear stress applied to the fluid is inversely proportional to the velocity gradient (du/dy)
c. the shear stress applied to the fluid is directly proportional to the specific weight of the fluid
d. the shear stress applied to the fluid is inversely proportional to the specific weight of the fluid
ANSWER: the shear stress applied to the fluid is directly proportional to the velocity
gradien
12) What is an ideal fluid?
a. A fluid which has no viscosity
b. A fluid which is incompressible
c. A fluid which has no surface tension
d. All of the above
ANSWER: All of the above
13) The below diagram is a graph of change in shear stress with respect to velocity
gradient in a fluid. What is a type of the fluid?



a. Newtonian fluid
b. Non-Newtonian fluid
c. Ideal fluid
d. Dilatent fluid
ANSWER: Non-Newtonian fluid
14) The fluid will rise in capillary when the capillary is placed in fluid, if
a. the adhesion force between molecules of fluid and tube is less than the cohesion between
liquid molecules
b. the adhesion force between molecules of fluid and tube is more than the cohesion between
liquid molecules
c. the adhesion force between molecules of fluid and tube is equal to the cohesion between liquid
molecules
d. cannot say
ANSWER: the adhesion force between molecules of fluid and tube is more than the
cohesion between liquid molecules
15) When the angle between surface tension with the liquid (θ) is greater than 90o, the
liquid becomes
a. flat
b. concave upward
c. convex upward
d. unpredictable
ANSWER: convex upward
16) If stream function (Ψ) satisfies the Laplace equation, it is a possible case of
a. a circular flow
b. a rotational flow
c. an irrotational flow
d. none of the above
ANSWER: an irrotational flow
17) Which acceleration has a nonzero value in uniform flow?
a. Local acceleration
b. Convective acceleration
c. Both local as well as convective acceleration
d. unpredictable
ANSWER: Local acceleration
18) Viscous forces are not present in
a. rotational flow
b. irrotational flow
c. laminar flow
d. none of the above
ANSWER: irrotational flow
19) The component of acceleration due to change in the direction of velocity vector is
called as
a. direction acceleration
b. tangential acceleration
c. normal acceleration
d. cannot say
ANSWER: normal acceleration
20) Blood circulation through arteries is
a. a laminar flow
b. a turbulent flow
ANSWER: a laminar flow
21) What is the correct formula for Euler's equation of motion?
Where,
ρ = density of the fluid
p = pressure force
g = acceleration due to gravity
v = velocity of the fluid
a. (∂p / ρ) + (∂g / ρ) + (∂v / ρ) = 0
b. (∂p / ρ) + (∂g / ρ) + (v dv) = 0
c. (∂p / ρ) + (g dz) + (v dv) = 0
d. (p dp) + (g dz) + (v dv) = 0
ANSWER: (∂p / ρ) + (g dz) + (v dv) = 0
22) Which of the following sentences are true for Bernoulli's equation?
1. Bernoulli's principle is applicable to ideal incompressible fluid
2. The gravity force and pressure forces are only considered in Bernoulli's principle
3. The flow of fluid is rotational for Bernoulli's principle
4. The heat transfer into or out of fluid should be zero to apply Bernoulli's principle
a. (1), (2) and (3)
b. (1), (3) and (4)
c. (1), (2) and (4)
d. (1), (2), (3) and (4)
ANSWER: (1), (2) and (4)
23) Which of the following devices does not use Bernoulli's equation as its working
principle?
a. Venturimeter
b. Orifice-meter
c. Pitot tube
d. None of the above
ANSWER: None of the above
24) Venturimeter consists of short converging conical tube which has a total inclination
angle of
a. 11 ± 1o
b. 21 ± 1o
c. 30 ± 1o
d. 60 ± 1o
ANSWER: 21 ± 1o
25) The cylindrical portion of short length, which connects converging and diverging
section of venturimeter, is called as
a. diffuser
b. connector
c. throat
d. manometer tube
ANSWER: throat