300+ REAL TIME Fluid Mechanics Objective Questions & Answers 2023

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:

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:

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:

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:

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:

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:

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:

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:

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:

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:

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:

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:

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

250+ TOP MCQs on Metacentre and Metacentric Height and Answers

Fluid Mechanics Multiple Choice Questions on “Metacentre and Metacentric Height”.

1. A rectangular pontoon is 5 m long, 3 m wide and 1.40 m high. The depth of immersion of the pontoon is 0.60 m in seawater. If the centre of gravity is 0.7 m above the bottom of the pontoon, determine the metacentric height. The density for seawater = 1045 kg/m³.
a) 0.135
b) 0.271
c) 0.543
d) 0.068
Answer: a
Clarification: BG=Centre of pontoon – Centre of immersed portion=0.7-0.3=0.4
Metacentric height=I/∀ -BG
I=bd³/12 = 5*3³/12
∀=5*3*1.4
Metacentric height=0.135 m.

2. A uniform body of size 4 m long * 2.5 m wide * 1.5 m deep floats in water. What is the weight of the body if depth of immersion is 1 m ?
a) 147.1 kN
b) 294.3 kN
c) 73.5 kN
d) 588.6 kN
Answer: a
Clarification: Weight of Body = Weight of water displaced
= ρ*g*Volume of displaced water=9.81*1000*4*2.5*1.5=147.1kN.

3. A block of material of specific gravity 0.45 floats in water. Determine the meta-centric height of the block if its size is 3 m * 2 m* 0.8 m.
a) 0.506 m
b) 0.376 m
c) 1.012 m
d) 0.127 m
Answer: b
Clarification: BG= Centre of pontoon – Centre of immersed portion=0.4 – 0.55*0.8=0.04
Metacentric height=I/∀ -BG
I=bd³/12 = 3*2³/12
∀=3*2*0.8
Metacentric height=0.376 m.

4. A solid cylinder of diameter 4.5 has a height of 2.5 metres. Find the meta-centric height of the cylinder when it is floating in water with its axis vertical. The sp. gr. of the cylinder=0.45.
a) 1.9 m
b) 3.8 m
c) 5.7 m
d) .95 m
Answer: a
Clarification:BG= Centre of pontoon – Centre of immersed portion=1.25-0.45*2.5=0.125
Metacentric height=I/∀ -BG
I=π*r⁴
∀= π*r*r*h
Metacentric height=1.9 m.

5. In case of spherically shaped bodies of uniform mass distribution and completely immersed in fluid and floating, the centre of buoyancy coincides with centre of gravity.
a) True
b) False
Answer: a
Clarification: The volume of fluid displaced by the body is equal to the actual volume of body in air. Hence, In case of spherically shaped bodies of uniform mass distribution and completely immersed in fluid and floating, the centre of buoyancy coincides with centre of gravity.

6. Proper explanation for metacentre is:
a) Point at which line of action of force meets the normal axis of body when it is given angular displacement
b) Intersection of line passing through new centre of buoyancy and centre of gravity.
c) point about which body starts oscillating when it is given small angular displacement
d) All of the mentioned
Answer: d
Clarification: All of the above explanation are apt.

7. The metacentric height is affected by the change in density.
a) True
b) False
Answer: True
Clarification: Metacentre does depend on the density. Hence, the metacentric height is affected by the change in density.

8.For a completely immersed body, the metacentric height is always zero.
a) True
b) False
Answer: b
Clarification: The metacentric height may or may not be zero as metacentre will not always coincide with centre of gravity.

9. Meta centre always lies below the centre of gravity
a) True
b) False
Answer: b
Clarification: It depends on the stability of floating body.

10. The principle of floatation of bodies is based on the premise of
a) Metacentre
b) Newtons first law
c) Newtons law of viscosity
d) None of the mentioned
Answer: a
Clarification: The principle of floatation of bodies is based on the premise of Metacentre.

250+ TOP MCQs on Bernoulli’s Equation for Real Fluids and Applications of Bernoulli’s Equation and Answers

Fluid Mechanics Question Bank on “Bernoulli’s Equation for Real Fluids & Applications of Bernoulli’s Equation”.

1. Which is the cheapest device for measuring flow / discharge rate.
a) Venturimeter
b) Pitot tube
c) Orificemeter
d) None of the mentioned
Answer: c
Clarification: Orificemeter is the cheapest available device for measuring flow/discharge rate.

2. The principle of Orificemeter is same as that of Venturimeter.
a) True
b) False
Answer: a
Clarification: The working principle for both Orificemeter and Venturimeter is same.

3. What is the relationship between Orificemeter diameter and pipe diameter
a) Orificemeter diameter is 0.5 times the pipe diameter
b) Orificemeter diameter is one third times the pipe diameter
c) Orificemeter diameter is one fourth times the pipe diameter
d) Orificemeter diameter is equal to the pipe diameter
Answer: c
Clarification: None.

4. The Orificemeter readings are more accurate than Venturimeter.
a) True
b) False
Answer: b
Clarification: The Venturimeter readings are more accurate than Orificemeter.

5. The Orificemeter readings are more accurate than Pitot tube readings.
a) True
b) False
Answer: b
Clarification: The Pitot tube readings are more accurate than Orificemeter.

6. The Orificemeter has a smooth edge hole.
a) True
b) False
Answer: b
Clarification: The Orificemeter has a rough edge hole.

7. A nanometre is connected to a section which is at a distance of about 4 to 6 times the pipe diameter upstream from orifice plate.
a) True
b) False
Answer: b
Clarification: A manometre is connected to a section which is at a distance of about 1.5 to 2.0 times the pipe diameter upstream from orifice plate.

8. Venturimeter is based on integral form of Euler’s equation.
a) True
b) False
Answer: a
Clarification: Venturimeter is based on Bernoulli’s equation.

9. Orifice Meter can only be used for measuring rate of flow in open pipe like structure.
a) True
b) False
Answer: a
Clarification: Orificemetre can only be used for measuring rate of flow in an enclosed pipe like structure.

10. Orifice meter consists of a flat rectangular plate.
a) True
b) False
Answer: b
Clarification: Orifice meter consists of a flat circular plate.

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250+ TOP MCQs on Hydraulic Gradient and Total Energy Line and Answers

Fluid Mechanics Problems on “Hydraulic Gradient and Total Energy Line”.

1. Energy gradient line takes into consideration
a) potential and kinetic heads only
b) potential and pressure heads only
c) kinetic and pressure heads only
d) potential, kinetic and pressure heads

Answer: d

2. Hydraulic gradient line takes into consideration
a) potential and kinetic heads only
b) potential and pressure heads only
c) kinetic and pressure heads only
d) potential, kinetic and pressure heads

Answer: b
Clarification: HGL is obtained by plotting piezometric head at various points along the axis of the pipe.
H_p = P ⁄ γ + z
where H_p is the piezometric head, P ⁄ γ is the pressure head and z is the potential head.

3. Which of the following is true?
a) EGL always drops in the direction of c
b) EGL always rises in the direction of flow
c) EGL always remains constant in the direction of flow
d) EGL may or may not in the direction of flow

Answer: a
Clarification: EGL is obtained by plotting total head at various points along the axis of the pipe. Since the total head decreases in the direction of flow, EGL will always drop in that direction.

4. Which of the following is true?
a) HGL always drops in the direction of flow
b) HGL always rises in the direction of flow
c) HGL always remains constant in the direction of flow
d) HGL may or may not in the direction of flow

Answer: d
Clarification: HGL is obtained by plotting piezometric head at various points along the axis of the pipe. Since pressure may either rise or fall in the direction of flow, HGL may or may not change in that direction.

5. Which of the following is true?
a) HGL will never be above EGL
b) HGL will never be under EGL
c) HGL will never coincide with EGL
d) HGL will may or may not be above EGL

Answer: a

6. The vertical intercept between EGL and HGL is equal to
a) pressure head
b) potential head
c) kinetic head
d) Piezometric head

Answer: c

7. The slope of HGL will be
a) greater than that of EGL for a pipe of uniform cross-section
b) smaller than that of EGL for a pipe of uniform cross-section
c) equal than that of EGL for a pipe of uniform cross-section
d) independent of that of EGL for a pipe of uniform cross-section

Answer: c
Clarification: The vertical intercept between EGL and HGL is equal to the kinetic head. For a pipe of uniform cross-section, there will be no change in the velocity of flow across the pipe. Since the kinetic head remian constant, the slope of HGL will be equal than that of EGL.

8. For a nozzle, the vertical intercept between EGL and HGL
a) increases
b) decreases
c) remains constant
d) may increase or decrease

Answer: a
Clarification: The vertical intercept between EGL and HGL is equal to the kinetic head. For a nozzle, the cross-sectional area decreases in the direction of flow leading to an increase in the velocity of flow across the pipe. Since the kinetic head increases, the vertical intercept between EGL and HGL will increase.

9. For a diffuser, the vertical intercept between EGL and HGL
a) increases
b) decreases
c) remains constant
d) may increase or decrease

Answer: b
Clarification: The vertical intercept between EGL and HGL is equal to the kinetic head. For a diffuser, the cross-sectional area increases in the direction of flow leading to a decrease in the velocity of flow across the pipe. Since the kinetic head decreases, the vertical intercept between EGL and HGL will decrease.

10. Which of the following is true?
a) the slope of EGL will always be greater than that of the axis of the pipe
b) the slope of EGL will always be smaller than that of the axis of the pipe
c) the slope of EGL will always be equal to that of the axis of the pipe
d) the slope of EGL will always be independent of that of the axis of the pipe

Answer: d

250+ TOP MCQs on Separation of Boundary Layer and Answers

Fluid Mechanics Multiple Choice Questions on “Separation of Boundary Layer”.

1. How can we determine whether the flow is laminar or turbulent?
a) Reynold’s number
b) Mach number
c) Froude number
d) Knudsen number
Answer: a
Clarification: Reynold’s number is used to determine whether the flow is laminar or turbulent. If Reynold’s number is less than 2000, it is a laminar flow. If Reynold’s number is greater than 2000, then it is a turbulent flow.

2. The flow separation occurs when the fluid travels away from the __________
a) Surface
b) Fluid body
c) Adverse pressure gradient
d) Inter-molecular spaces
Answer: c
Clarification: Adverse pressure gradient takes place when the static pressure increases. It increases the direction of the flow. Adverse pressure gradient plays an important role in flow separation. Thus, option c is correct.

3. The swirl caused due to eddies are called as ______
a) Vortices
b) Vertices
c) Volume
d) Velocity
Answer: a
Clarification: Vortices are a region in a fluid. It takes place when the flow revolves around an axis line. Vortices can be straight or curved. They form shapes like smoke rings and whirlpools.

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. Which among the following is a device that converts a laminar flow into a turbulent flow?
a) Dead Weight Gauge
b) Vacuum Gauge
c) Turbulator
d) Ionization Gauge
Answer: c
Clarification: Turbulator is a device that converts a laminar flow into a turbulent flow. The turbulent flow can be desired parts of an aircraft or also in industrial applications. Turbulator is derived from the word “turbulent”.

6. Boundary layer separation does not undergo detachment.
a) True
b) False
Answer: b
Clarification: Boundary layer separation undergoes detachment from the surface into a broader wake. It occurs mainly when the portion of the boundary layer is closest to the wall. It leads to reverse in the flow direction.

7. With the boundary layer separation, displacement thickness________
a) Increases
b) Decreases
c) Remains Same
d) Independent
Answer: a
Clarification: With the boundary layer separation, displacement thickness increases sharply. This helps to modify the outside potential flow and its pressure field. Thus, option ‘a’ is the correct choice.

8. What is the instrument used for the automatic control scheme during the fluid flow?
a) Rotameters
b) Pulley plates
c) Rotary Piston
d) Pilot Static Tube
Answer: d
Clarification: Pilot static tube is a system that uses an automatic control scheme to detect pressure. It has several holes connected to one side of the device. These outside holes are called as a pressure transducer, which controls the automatic scheme during fluid flow.

9. What is D’Alembert’s Paradox?
a) Resistance= 0
b) Drag force= 0
c) Temperature = 0
d) Pressure gradient= 0
Answer: b
Clarification: D’Alembert’s Paradox states that for an incompressible and inviscid flow potential flow, the drag force is equal to zero. The fluid is moving at a constant velocity with respect to its relative fluid.

10. The steady- state flow must satisfy ___________
a) Kirchhoff’s law
b) Newtons law
c) Rutherford’s experiment
d) Kepler’s law
Answer: a
Clarification: The steady state flow must satisfy Kirchhoff’s first and second law. The first law states that the total flow into the junction equals the total flow away from the junction. Second law is called as the law of conservation of mass. It states that between two junctions, the head loss is independent of the path followed.