Category: Fluid Mechanics Objective Questions

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.

250+ TOP MCQs on Impulse Momentum Equation and Answers

Fluid Mechanics Multiple Choice Questions on “Impulse Momentum Equation”.

1. When a cricket bat hits a cricket ball, impulse is applied on the_________
a) Bat
b) Ball
c) Bat and ball
d) No impulse is applied
Answer: b
Clarification: Time passes as force is applied on an object. The bat applies the force on the ball for a short period of time. By this way, we can say in accordance to the Newton’s third law forces come in pairs. So, the ball also applies a force on the bat, therefore it has an impulse applied to it.

2. Momentum is a ______ quantity
a) Scalar
b) Vector
c) Infinite
d) Zero
Answer: b
Clarification: Momentum is a vector quantity as it has both size and direction. Size of the momentum is equal to the mass of the object into the size of the objects velocity. The direction of objects velocity is the same as the direction of the momentum.

3. The equation for impulse is_______
a) F∆t=m∆v
b) F∆t=mu
c) F∆t=mT
d) F∆t=mRT
Answer: a
Clarification: Impulse is equal to the net force times the length of time over which the force is applied on the body of the fluid. On the right hand side, we have the change in momentum. Thus, option ‘a’ is the most suitable one.

4. What is the SI unit of impulse?
a) N/m
b) N/m2
c) N.s
d) Kg.m
Answer: c
Clarification: The SI unit of impulse is Newton second. It is given by the linear momentum due to the vector change. This produces an impulse in the same direction with respect to a given time.

5. What is the SI unit of momentum?
a) kgm/s
b) kgm/s2
c) kgm/s3
d) kg.m2
Answer: a
Clarification: The SI unit of momentum is given by the product of the units of mass and velocity. In SI units, (mass is in kg) and (velocity is in m/s). As we know that momentum is mass times velocity. The unit turns out to be kgm/s.

6. Change in momentum of an object is equal to the_______
a) Internal Energy
b) Entropy
c) Impulse
d) Enthalpy
Answer: c
Clarification: The mass is distributed over two velocities. According to the Newton’s second law, the change in momentum is equal to the impulse so produced. Since, momentum is a quantity that describes an object’s resistance to stopping. It is equated with its impulse.

7. What is the unit of specific impulse?
a) m/s
b) m2/s
c) m3/s
d) m/s2
Answer: a
Clarification: Specific impulse is equal to the exhaust velocity of the fluid. Since, the unit of exhaust velocity is m/s, the unit of specific impulse is also the same. It is used to measure the efficacy of rocket propellants.

8. What is the formula to find specific impulse?
a) Jsp=m/v
b) Jsp= J/m
c) Jsp=T/m
d) Jsp=J/q
Answer: b
Clarification: Specific impulse is defined as impulse per weight. It can also be defined as thrust per weight of a flow rate. It is equal to the exhaust velocity divided by acceleration due to gravity. (SI Unit: m/s)

9. Angular momentum is a _______ quantity
a) Scalar
b) Vector
c) Infinite
d) Finite
Answer: b
Clarification: Angular momentum is a vector quantity as it has both size and direction. Size of the momentum is equal to the mass of the object into the size of the object’s velocity. The direction of objects velocity is the same as the direction of the momentum.

10. Angular momentum is proportional to __________
a) Inertia and angular speed
b) Mass and angular speed
c) Angular speed and volume
d) Rate of change of angular speed
Answer: a
Clarification: Moment of inertia is not only dependent on the amount of matter. It also depends upon the position of axis of rotation and the shape of the matter. (Formula: L=Iω). Thus, inertia and angular speed play an important role in determining the angular momentum.

250+ TOP MCQs on Loss of Energy in Pipes and Answers

Fluid Mechanics Multiple Choice Questions on “Loss of Energy in Pipes”.

1. Which one of the following is a major loss?
a) frictional loss
b) shock loss
c) entry loss
d) exit loss

Answer: a
Clarification: The major loss for the flflow through the pipes is due to the frictional resistance between adjacent fluid layers sliding over each other. All other losses are considered to be minor losses.

2. Which property of the fluid accounts for the major losses in pipes?
a) density
b) specific gravity
c) viscosity
d) compressibility

Answer: c
Clarification: The major loss for the flow through the pipes is due to the frictional resistance between adjacent fluid layers sliding over each other. This resistance arises due to the presence of viscous property of the fluid.

3. The frictional resistance for fluids in motion is
a) proportional to the velocity in laminar flow and to the square of the velocity in turbulent flow
b) proportional to the square of the velocity in laminar flow and to the velocity in turbulent flow
c) proportional to the velocity in both laminar flow and turbulent flow
d) proportional to the square of the velocity in both laminar flow and turbulent flow

Answer: a
Clarification: According to the laws of fluid friction, rf / v (for steady streamline flow) and rf / v2(for turbulent flow), where rf is the frictional resistance and v is the velocity of flow.

4. The frictional resistance for fluids in motion is
a) dependent on the pressure for both laminar and turbulent flows
b) independent of the pressure for both laminar and turbulent flows
c) dependent on the pressure for laminar flow and independent of the pressure for turbulent flow
d) independent of the pressure for laminar flow and dependent on the pressure for turbulent flow

Answer: b
Clarification: According to the laws of fluid friction, the frictional resistance is independent of the pressure for both laminar and turbulent flows.

5. The frictional resistance for fluids in motion is
a) inversely proportional to the square of the surface area of contact
b) inversely proportional to the surface area of contact
c) proportional to the square of the surface area of contact
d) proportional to the surface area of contact

Answer: d
Clarification: According to the laws of fluid friction, the frictional resistance is proportional to the surface area of contact for both laminar and turbulent flows.

6. The frictional resistance for fluids in motion varies
a) slightly with temperature for both laminar and turbulent flows
b) considerably with temperature for both laminar and turbulent flows
c) slightly with temperature for laminar flow and considerably with temperature for turbulent flow
d) considerably with temperature for laminar flow and slightly with temperature for turbulent flow

Answer: d
Clarification: According to the laws of fluid friction, the frictional resistance for fluids in motion varies considerably with temperature for laminar flow and slightly with temperature for turbulent flow.

7. Which one of the follflowing is correct?
a) the frictional resistance depends on the nature of the surface area of contact
b) the frictional resistance is independent of the nature of the surface area of contact
c) the frictional resistance depends on the nature of the surface area of contact for laminar flows but is independent of the nature of the surface area of contact for turbulent flows
d) the frictional resistance is independent of the nature of the surface area of contact for laminar flows but depends on the nature of the surface area of contact for turbulent flows

Answer: d
Clarification: According to the laws of fluid friction, the frictional resistance is independent of the nature of the surface area of contact for laminar flows but depends on the nature of the surface area of contact for turbulent flows.

8. Which one of the follflowing is correct?
a) the frictional resistance is always dependent on the nature of the surface area of contact
b) the frictional resistance is always independent of the nature of the surface area of contact
c) the frictional resistance is dependent on the nature of the surface area of contact when the liquid flows at a velocity less than the critical velocity
d) the frictional resistance is independent of the nature of the surface area of contact when the liquid flows at a velocity less than the critical velocity

Answer: d
Clarification: Frictional resistance is dependent on the nature of the surface area of contact. But, when the liquid flows at a velocity less than the critical velocity, a thin stationary film of the liquid is formed on the supporting surface. Hence, the frictional resistance becomes independent of the nature of the surface of contact.

9. Which one of the follflowing is correct?
a) Darcy-Weisbach’s formula is generally used for head loss in flow through both pipes and open channels
b) Chezy’s formula is generally used for head loss in flow through both pipes and open channels
c) Darcy-Weisbach’s formula is generally used for head loss in flow through both pipes and Chezy’s formula for open channels
d) Chezy’s formula is generally used for head loss in flow through both pipes and Darcy-Weisbach’s formula for open channels

Answer: c
Clarification: Darcy-Weisbach’s formula is generally used for head loss in flow through both pipes as it takes into consideration the flow velocity whereas Chezy’s formula is used for open channels as it considers the pressure difference.

10. A liquid flows through pipes 1 and 2 with the same flow velocity. If the ratio of their pipe diameters d1 : d2 be 3:2, what will be the ratio of the head loss in the two pipes?
a) 3:2
b) 9:4
c) 2:3
d) 4:9

Answer: c

11. A liquid flowss through two similar pipes 1 and 2. If the ratio of their flow velocities v1 : v2 be 2:3, what will be the ratio of the head loss in the two pipes?
a) 3:2
b) 9:4
c) 2:3
d) 4:9

Answer: d

12. A liquid flows with the same velocity through two pipes 1 and 2 having the same diameter. If the length of the second pipe be twice that of the first pipe, what should be the ratio of the head loss in the two pipes?
a) 1:2
b) 2:1
c) 1:4
d) 4:1

Answer: a

13. The head loss at the entrance of the pipe is that at it’s exit
a) equal to
b) half
c) twice
d) four times

Answer: b

14. On which of the factors does the co-efficent of bend in a pipe depend?
a) angle of bend and radius of curvature of the bend
b) angle of bend and radius of the pipe
c) radius of curvature of the bend and pipe
d) radius of curvature of the bend and pipe and angle of bend

Answer: d
Clarification: The co-efficent of bend in a pipe depends on all the three parameters – radius of curvature of the bend, diameter (radius) of the pipe and angle of bend.

250+ TOP MCQs on Turbulent Boundary Layer on a Flat Plate and Answers

Fluid Mechanics Multiple Choice Questions on “Turbulent Boundary Layer on a Flat Plate”.

1. The main property that affects a boundary layer is__________
a) Temperature
b) Pressure
c) Viscosity
d) Surface tension
Answer: c
Clarification: A boundary layer is an important concept that refers to the layer of fluid. The fluid that is in the immediate vicinity of a bounding surface. The main property that affects a boundary layer is viscosity.

2. The layer that is influenced by a planetary boundary is called______
a) Atmospheric boundary layer
b) Lithosphere
c) Troposphere
d) Hydrosphere
Answer: a
Clarification: The planetary boundary layer is also called as atmospheric boundary layer(ABL). It is the lowest part of the atmosphere. The behaviour of ABL is directly influenced by its contact with the planetary surface.

3. What is the other name for Stoke’s boundary layer?
a) Momentum boundary layer
b) Atmospheric boundary layer
c) Oscillatory boundary layer
d) Thermal boundary layer
Answer: c
Clarification: Stoke’s boundary layer is also called as Oscillatory boundary layer. It is a boundary layer that is close to a solid wall. It moves in an oscillatory motion. It arrested by a viscous force acting in the opposite direction.

4. Eddy viscosity is a turbulent transfer of_________
a) Fluid
b) Heat
c) Momentum
d) Pressure
Answer: c
Clarification: Eddy viscosity is a turbulent transfer of momentum by eddies. It gives rise to an internal fluid friction. It is in analogous to the action of molecular viscosity in laminar fluid flow. Eddy viscosity takes place on a large scale.

5. The laminar boundary layer is a _________
a) Smooth flow
b) Rough flow
c) Uniform flow
d) Random flow
Answer: a
Clarification: For a laminar boundary layer the fluid moves in a very smooth flow. The laminar flow creates less skin friction drag. It is a less stable flow. The laminar boundary layer has got an increase in its thickness.

6. The turbulent boundary layer is a _________
a) Non-uniform with swirls
b) Uniform
c) Less stable
d) Smooth
Answer: a
Clarification: For a turbulent boundary layer the fluid moves in different direction producing swirls. It has more skin friction drag than that of laminar boundary layer. It is more stable when compared to laminar.

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. How does a turbulent boundary layer produce swirls?
a) Due to random motion
b) Collision of molecules
c) Due to eddies
d) Due to non-uniform cross section
Answer: c
Clarification: For a turbulent boundary layer the fluid moves in different direction producing swirls. It produces swirls due to the presence of eddies. The smooth laminar boundary layer flow breaks down and transforms to a turbulent flow.

9. Define Viscosity.
a) Resistance to flow of object
b) Resistance to flow of air
c) Resistance to flow of fluid
d) Resistance to flow of heat
Answer: c
Clarification: Viscosity is developed due to the relative motion between two surfaces of fluids at different velocities. It happens due to the shear stress developed on the surface of the fluid.

10. The continuity equation of two- dimensional steady incompressible flow is_______
fluid-mechanics-questions-answers-turbulent-layer-plate-q10
Answer: a
Clarification: The continuity equation of two- dimensional steady incompressible flow is fluid-mechanics-questions-answers-turbulent-layer-plate0q10-exp. It is in accordance with the Navier- Stokes equations for a two- dimensional steady incompressible flow in cartesian coordinates.

250+ TOP MCQs on Manning’s Equation – 1 and Answers

Fluid Mechanics Multiple Choice Questions on “Manning’s Equation – 1”.

1. A rectangular channel is having depth 2m and width 3m, bed slope of 1 in 700. The value of manning’s roughness co efficient (n) is 0.06, estimate the discharge through the channel.
a) 2.42m3⁄s
b) 3.42m3⁄s
c) 4.42m3⁄s
d) 5.42m3⁄s
Answer: b
Clarification: fluid-mechanics-questions-answers-mannings-equation-1-q1

2. Estimate the discharge through a triangular channel having depth 7m and side slope 1H:5V in which the bed slope is 1 in 1000. Manning’s co efficient = 0.03.
a) 8.07m3⁄s
b) 9.07m3⁄s
c) 10.07m3⁄s
d) 11.07m3⁄s
Answer: a
Clarification: fluid-mechanics-questions-answers-mannings-equation-1-q2

3. The base width and the depth of a trapezoidal channel is 9m and 5m respectively. Calculate the discharge through a channel if the side slope of the channel is 1H:4V and the bed slope is 1 in 500. (n=0.04)
a) 109.73m3⁄s
b) 110.73m3⁄s
c) 111.73m3⁄s
d) 112.73m3⁄s
Answer: a
Clarification:
fluid-mechanics-questions-answers-mannings-equation-1-q3

4. A circular channel section has diameter of 6m and it is running half. Calculate the discharge through the channel if the bed slope is 1 in 600 and manning’s co efficient is equal to 0.014.
a) 52m3⁄s
b) 53m3⁄s
c) 54m3⁄s
d) 55m3⁄s
Answer: c
Clarification:
fluid-mechanics-questions-answers-mannings-equation-1-q4

5. The diameter of a circular channel section which is running full is 8m. Determine the discharge through the channel section if the bed slope is 1 in 600 and the value of the manning’s co efficient is 0.013.
a) 249.45m3⁄s
b) 250.45m3⁄s
c) 251.45m3⁄s
d) 252.45m3⁄s
Answer: b
Clarification:
fluid-mechanics-questions-answers-mannings-equation-1-q5

6. The area of a channel section is 8m2 and the wetted perimeter is 8m. Calculate the value of the bed slope of the channel if the discharge is 33.33m3⁄s and manning’s co efficient is 0.012.
a) 1 in 300
b) 1 in 400
c) 1 in 500
d) 1 in 600
Answer: b
Clarification:fluid-mechanics-questions-answers-mannings-equation-1-q6

7. The area of the triangular section is 66.67m2 and the wetted perimeter of the section is 24.03m. Calculate the value of the manning’s roughness co efficient if the bed slope of the channel section is 1 in 500 and the discharge through the channel is 117.61m3⁄s.
a) 0.03
b) 0.04
c) 0.05
d) 0.06
Answer: c
Clarification:fluid-mechanics-questions-answers-mannings-equation-1-q7

8. The discharge through a trapezoidal channel is 245.06m3⁄s and the bed slope is 1 in 1000. Calculate the value of the wetted area if the hydraulic radius is 2.26m. Manning’s roughness co efficient = 0.008.
a) 34m2
b) 35m2
c) 36m2
d) 37m2
Answer: c
Clarification:
fluid-mechanics-questions-answers-mannings-equation-1-q8

9. Determine the value of manning’s constant for a rectangular channel if Chezy’s constant is equal to 50 and the depth and widths of the channel are 4m and 7m respectively.
a) 0.012
b) 0.022
c) 0.032
d) 0.042
Answer: b
Clarification: fluid-mechanics-questions-answers-mannings-equation-1-q9

10. The side slope of a triangular channel section is 1H:4V and the depth is 12m. Calculate the value of chezy’s constant if the value of manning’s constant is 0.03.
a) 32.48
b) 33.48
c) 34.48
d) 35.48
Answer: d
Clarification: fluid-mechanics-questions-answers-mannings-equation-1-q10

11. Determine the value of Chezy’ s constant for a trapezoidal channel having depth 3m, base width 11m, side slope 1H:3V and the manning’s co efficient is 0.012.
a) 94.15
b) 94.25
c) 94.35
d) 94.45
Answer: a
Clarification:
fluid-mechanics-questions-answers-mannings-equation-1-q11

12. Estimate the value of the manning’s constant for a fully running circular section having diameter of 8m and the value of Chezy’s constant is 50.
a) 0.022
b) 0.032
c) 0.042
d) 0.052
Answer: a
Clarification:
fluid-mechanics-questions-answers-mannings-equation-1-q12

250+ TOP MCQs on Compressibility and Bulk Modulus and Answers

Fluid Mechanics Multiple Choice Questions on “Compressibility and Bulk Modulus”.

1. Which one of the following is the correct relation between compressibility β and Bulk Modulus k
a) β = k
b) β = 1/k
c) β = 2k
d) β = k/2

Answer: b
Clarification: Compressibility β of a liquid is deβned as the ratio of volumetric strain to the compressive stress while Bulk Modulus is the ratio of compressive stress to volumetric strain. Hence, β = 1/k is the correct relation.

2. Which one of the following is true about Bulk Modulus of elasticity?
a) it is the ratio of compressive stress to volumetric strain
b) it is the ratio of compressive stress to linear strain
c) it is the ratio of tensile stress to volumetric strain
d) it is the ratio of tensile stress to linear strain

Answer: a
Clarification: Bulk Modulus k is related to the compression of a liquid and the decrease in volume per unit volume. It is the ratio of compressive stress to the volumetric strain.

3. The value of the Bulk Modulus of elasticity for an incompressible fluid is
a) zero
b) unity
c) infinity
d) very low

Answer: c
Clarification: k = 1/β, where k= Bulk Modulus of elasticity and β= compressibility. For an incompressible fluid, β=0, thus the value of k will tend to infinity.

4. Three fluids 1, 2 and 3 have Bulk Moduli of k1, k2 and k3 respectively. If k1 > k2 > k3, which liquid will have the highest compressibility?
a) liquid 1
b) liquid 2
c) liquid 3
d) they’ll have equal compressibilities

Answer: c
Clarification: k = 1=β, where k= Bulk Modulus of elasticity and β= compressibility. If k1 > k2 > k3, then β1 < β2 < β3. Thus, liquid 3 will have the highest compressibility.

5. Bulk Modulus, Pressure, Force, Stress – Which one of these won’t have the same unit as the others?
a) Bulk Modulus
b) Pressure
c) Force
d) Stress

Answer: c
Clarification: The SI unit of Bulk Modulus, Pressure and Stress is N/m2 but the unit of Force is N.

6. Which of the following is the dimension of Bulk Modulus?
a) [M1L-1T-1].
b) [M1L-1T-2].
c) [M1L1T-2].
d) [M1L1T-1].

Answer: b

7. Which one of the following is the unit of compressibility?
a) m=N
b) m2=N
c) m3=N
d) it is unitless

Answer: b

8. Which of the following is the dimension of compressibility?
a) [M1L1T-2].
b) [M1L1T-1].
c) [M-1L1T-2].
d) [M-1L1T2].

Answer: d