300+ REAL TIME Fluid Mechanics Objective Questions & Answers 2023

Fluid Mechanics Multiple Choice Questions & Answers on “Conditions of Equilibrium of a Floating and Submerged Bodies”.

1. A solid cylinder of diameter 5.0 m has a height of 6.0 m. Find the meta-centric height of the cylinder if the specific gravity of the material of cylinder 0.45 and it is floating in water with its axis vertical. State whether the equilibrium is stable or unstable.
a) -0.29 m
b) -0.61 m
c) -1.16 m
d) 0.14 m
Answer: b
Clarification: BG=Centre of pontoon – Centre of immersed portion=0.3-0.45*0.3=1.65
Metacentric height=I/∀ -BG
I=π*r⁴=π*2.5⁴
∀=π*r*r*h=π*2.5*2.5*6
Metacentric height=-0.61.

2. A solid cylinder of 15 cm diameter and 40 cm long, consists of two parts made of different materials. The first part at the base is 1.5 cm long and of specific gravity=6.5. The other part of the cylinder is made of the material having specific gravity 0.75. State, if the it can float vertically in water.
a) It will float
b) It will not float
c) Data insufficient
d) None of the mentioned
Answer: a
Clarification: AG=(weight of base*distance of C.G from base point A) + (weight of upper part*distance of C.G from point A)/ )weight of base + weight of upper part)
= 14.52
By principle of buoyancy,
Weight of cylinder = Weight of water displaced
h=38.625
AB=19.31
BG=14.25-19.31= -4.79
GM= Metacentric height=I/∀ -BG
= 6.16
As metacentric height is positive, it will float.

3. A wooden cylinder of sp.gr. = 0.6 and circular in cross-section is required to float in oil(sp.gr. = 0.90). Find the L/D ratio for the cylinder to float with its longitudinal axis vertical in oil, where L is the height of cylinder and D is its diameter.
a) L/D<9/16
b) L/D<3/4
c) L/D<2/3
d) None of the mentioned
Answer: b
Clarification: By principle of buoyancy,
Weight of cylinder = Weight of water displaced
h=2L/3
AG=L/2
AB=L/3
BG=AG-AB=L/6
GM= Metacentric height=I/∀ – BG=3D2/32L-L/6

For stable equilibrium, GM should be positive
GM>0
i.e L/D<3/4.

4. A cylinder(uniform density distribution) of radius 3.0 m has a height of 9.0 m. The specific gravity of the material of cylinder 0.85 and it is floating in water with its axis vertical. State whether the equilibrium is stable or unstable.
a) Stable
b) Unstable
c) Insufficient Data
d) None of the mentioned
Answer: a
Clarification: BG=Centre of pontoon – Centre of immersed portion=0.3-0.45*0.3=1.65
Metacentric height=I/∀ -BG
I=π*r⁴=π*3⁴
∀=π*r*r*h=π*3*3*9
Metacentric height=0.325.

5. If the magnitude of dimension of a rectangular wooden block is length>breadth>height, then for it to float on the water, it should be immersed in what manner?
a) It should be immersed vertically such that length is partially immersed
b) It should be immersed horizontally such that breadth is partially immersed
c) It should be immersed such that height is partially immersed
d) None of the mentioned
Answer: b
Clarification: When it is immersed in such a manner where height is partially immersed, its stability is most as moment of inertia is most about that axis.

6. When body is completely or partially immersed in a fluid, how much its weight be distributed for it to be in stable equilibrium.
a) Around the lower part
b) Around the upper part
c) Is independent of weight distribution
d) None of the mentioned
Answer: a
Clarification: When the weight distribution is around the lower part, the centre of gravity is at lower portion and hence below the centre of buoyancy which is condition for stable equilibrium.

7. In unstable equilibrium what is the relation between forces?
a) Buoyancy force= Weight of body
b) Buoyancy force > Weight of body
c) Buoyancy force < Weight of body
d) None of the mentioned
Answer: a
Clarification: Fb=W and the the centre of buoyancy is below the centre of gravity.

8. The floating body is said to be in unstable equilibrium if the metacentre is below the centre of gravity.
a) True
b) False
Answer: b
Clarification: The floating body is said to be in unstable equilibrium if the metacentre is above the centre of gravity.

9. The floating body is said to be in neutraL equilibrium if the metacentre is above the centre of gravity.
a) True
b) False
Answer: b
Clarification: The floating body is said to be in unstable equilibrium if the metacentre coincides with the centre of gravity.

10. In stable equilibrium for completely submerged bodies what is the relation between forces?
a) Buoyancy force= Weight of body,the centre of buoyancy is below the centre of gravity.
b) Buoyancy force=Weight of body, the centre of buoyancy is above the centre of gravity.
c) Buoyancy force < Weight of body
d) None of the mentioned
Answer: b
Clarification: Fb=W and the the centre of buoyancy is above the centre of gravity.

To practice all areas of Fluid Mechanics,

Fluid Mechanics Questions and Answers for Entrance exams on “Classification of Orifice & Hydraulic Coefficients”.

1. When is orifice called ‘large orifice’?
a) If the head of liquid is less than 5 times the depth of orifice
b) If the head of liquid is less than 2.5 times the depth of orifice
c) If the head of liquid is less Hence, 4 times the depth of orifice
d) If the head of liquid is less than 1.5 times the depth of orifice
Answer: a
Clarification: It is the correct parametric definition for ‘large orifice’.

2. In case of any orifice, velocity always remains constant and hence discharge can be calculated.
a) True
b) False
Answer: b
Clarification: In case of large orifice, velocity always remains variable and hence discharge cannot be calculated.

3. Find the discharge through a rectangular orifice 2.2 m wide and 1.3 m deep fitted to a easier tank. The water level in a team is 2.5 m above the top edge of orifice.
a) 13.9 m³/s
b) 11.5 m³/s
c) 16.9 m³/s
d) 8.7 m³/s
Answer: a
Clarification: Q = 2/3 Cd *b*√2g* (H2^1.5 – H1^1.5)
Here,
H1 = 3.8
H2 = 2.5
b = 2.2
Hence, Q = 13.9 m3/s.

4. Find the discharge through a rectangular orifice 3.2 m wide and 1.7 m deep fitted to a easier tank. The water level in a team is 3.3 m above the top edge of orifice. Take Cd = 0.6
a) 29.4 m³/s
b) 58.5 m³/s
c) 67.9 m³/s
d) 78.7 m³/s
Answer: a
Clarification: Q = 2/3 Cd *b*√2g* (H2^1.5 – H1^1.5)
Here,
H1 = 5
H2 = 3.3
b = 3.2
Hence, Q = 29.4 m3/s.

5. Find the discharge through totally drowned orifice of width 2.3 m if the difference of water levels on both side of the orifice be 40 cm. The height of water from to and bottom of the orifice are 2.6 m and 2.75 m respectively.
a) .56 m³/s
b) .64 m³/s
c) .75 m³/s
d) .55 m³/s
Answer: a
Clarification: Q = Cd * b * (H2 – H1) √2gH
Here, b = 2.3
H2 = 2.75
H1 = 2.6
H = 40
Q = .56 m³/s.

6. Find the discharge through totally drowned orifice of width 3.3 m if the difference of water levels on both side of the orifice be 50 cm. The height of water from to and bottom of the orifice are 2.25 m and 2.67 m respectively.
a) 2.8 m³/s
b) 2.7 m³/s
c) 2.6 m³/s
d) 2.5 m³/s
Answer: a
Clarification: Q = Cd * b * (H2 – H1) √2gH
Here, b = 3.3
H2 = 2.67
H1 = 2.25
H = 50
Q = 2.6 m³/s.

7. A rectangular orifice of 2 m width and 1.2 m deep is fitted in one side of large tank. The easier level on one side of the orifice is 3m above the top edge of the orifice while on the other side of the orifice the water level is 0.5 m below it’s top edge. Calculate discharge if Cd = .64
a) 4.95 m³/s
b) 5.67 m³/s
c) 3.56 m³/s
d) 6.75 m³/s
Answer: a
Clarification: Clarification: Q = Cd * b * (H2 – H) √2gH
Here, b = 2
H2 = 4.2

H = 3.5
Q = 4.94 m³/s.

8. The time taken to empty the tank is independent of Cd but depends only on the height and acceleration due to gravity.
a) True
b) False
Answer: b
Clarification: The time taken to empty the tank is dependent on Cd as well as depends only on the height and acceleration due to gravity.

9. The discharge rate is independent of the height difference and dependent only on the height.
a) True
b) False
Answer: b
Clarification: The discharge rate is dependent of the height difference and dependent only on the height.

10. In case of submerged orifice the discharge is substantially dependent on temperature of fluid
a) True
b) False
Answer: b
Clarification: Discharge is dependent on temperature but minimally.

To practice all areas of Fluid Mechanics for Entrance exams,

Fluid Mechanics Multiple Choice Questions on “Pipes in Series”.

1. The liquid flowing through a series of pipes can take up__________
a) Pipes of different diameters
b) Pipes of the same diameters only.
c) Single pipe only
d) Short pipes only
Answer: a
Clarification: When pipes of different diameters are connected at its ends to form a pipe, this pipe so developed is called as pipes in series. They might not have to be of the same diameters. But, having the same diameters are better as it avoids the losses so developed.

2. What is the total loss developed in a series of pipes?
a) Sum of losses in each pipe only
b) Sum of local losses only
c) Sum of local losses plus the losses in each pipe
d) Zero
Answer: c
Clarification: When the pipes of different diameters are connected in series from end to end to form a pipe line. The total loss so developed is equal to the sum of local losses plus the losses in each pipe. The local losses are developed at the connection point.

3. The total head loss for the system is equal to_________
a) Pipe length
b) Pipe diameter
c) Width of the reservoir
d) Height difference of reservoirs
Answer: d
Clarification: Total head loss for a system is equal to the height difference of the reservoirs. Height difference is denoted by the letter ‘H’. Total head loss can be equated by summing it up with all the local losses and the losses at each pipe.

4. Which among the following is not a loss that is developed in the pipe?
a) Entry
b) Exit
c) Connection between two pipes
d) Liquid velocity
Answer: d
Clarification: Liquid velocity in the pipe is the velocity with which the liquid travels through different cross sections of the pipe. It is a vector field which is used to describe the motion of a continuum. The length of flow velocity vector is equal to the flow speed.

5. Which among the following is the correct formula for head loss?
a) Z₁-Z₂
b) C
c) T₂-T₁
d) S₂-S₁
Answer: a
Clarification: Total head loss for a system is equal to the height difference of the reservoirs. Height difference is denoted by the letter ‘H’. Total head loss can be equated by summing it up with all the local losses and the losses at each pipe. Here, the height difference between the reservoirs is Z₁-Z₂.

6. If the two reservoirs are kept at the same level, the head loss is _______
a) Z₁-Z₂
b) Zero
c) T₂-T₁
d) S₂-S₁
Answer: b
Clarification: Total head loss for a system is equal to the height difference of the reservoirs. Height difference is denoted by the letter ‘H’. The height difference between the reservoirs is Z₁-Z₂. Since they are of the same level, Z₁=Z₂. Therefore, head loss is zero.

7. How do we determine the total discharge through parallel pipes?
a) Add them.
b) Subtract them
c) Multiply them
d) Divide them
Answer: a
Clarification: Total discharge in parallel pipes are determined by adding the discharges so developed in individual pipes. If Q₁ is the discharge through pipe 1 and Q₂ is the discharge through pipe 2. Then the total discharge through parallel pipes is equal to Q₁+Q₂.

8. The pipe diameter is ________
a) Directly proportional to fluid density
b) Directly proportional to mass flow rate
c) Inversely proportional to mass flow rate
d) Directly proportional to fluid velocity
Answer: b
Clarification: The pipe diameter is directly proportional to mass flow rate of fluid. Pipe diameter can be calculated if volumetric flow rate and velocity are known. ‘D’ is inversely proportional to its velocity.

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. Coefficient of friction of a laminar flow is_________
a) R_e/16
b) R_e/64
c) 16/R_e
d) 64/R_e
Answer: c
Clarification: Coefficient of friction is defined as the value that shows relationship between force and the normal reaction. It is mainly used to find out an object’s normal force and frictional force. Thus, it is equal to 16/R_e.

Fluid Mechanics Multiple Choice Questions on “Drag on a Sphere”.

1. What is the dimension for drag coefficient?
a) Newton/s
b) m/s
c) kg/N
d) Dimensionless
Answer: d
Clarification: In fluid dynamics, the drag coefficient has no dimensions. It is a dimensionless quantity. Drag coefficient is used to quantify the resistance of an object in a fluid environment. It is mainly used in air and water.

2. Skin friction acts on the component of _________
a) Profile drag
b) Surface blade
c) Vane angles
d) Parallel movement
Answer: a
Clarification: Skin friction acts on the component of profile drag. Pressure drag is also called as form drag. It mainly arises because of the shape of the object. Thus, the correct answer is profile drag.

3. Bodies with a larger cross section will have________
a) Lower drag
b) Higher drag
c) Same drag
d) No drag
Answer: b
Clarification: Bodies with a larger cross section will have higher drag. Pressure drag is also called as form drag. It mainly arises because of the shape of the object. Thus, the correct option ‘b’.

4. Drag coefficient is denotes as_______
a) C_d
b) B_c
c) D_c
d) T_c
Answer: a
Clarification: In fluid dynamics, the drag coefficient has no dimensions. It is a dimensionless quantity. Drag coefficient is used to quantify the resistance of an object in a fluid environment. It is mainly used in air and water. It is denoted as C_d.

5. The drag coefficient of a complete structure such as an aircraft includes________
a) Form drag
b) Pressure drag
c) Interference drag
d) Induced drag
Answer: c
Clarification: The drag coefficient of a complete structure such as an aircraft includes interference drag. It results when an airflow around one part of an object. The two airflows must speed up in order to pass through the restricted area.

6. The drag coefficient is directly proportional to the ___________
a) Drag force
b) Mass density
c) Area
d) Flow speed
Answer: a
Clarification: The drag coefficient is directly proportional to the drag force. In fluid dynamics, the drag coefficient has no dimensions. It is a dimensionless quantity. Drag coefficient is used to quantify the resistance of an object in a fluid environment.

7. If the friction is neglected, then_______
a) V_r1 > V_r2
b) V_r1r2
c) V_r1 = V_r2
d) V_r1 is a zero
Answer: c
Clarification: The relative velocity of the jet is denoted as V_r1. It is the relative velocity at the inlet to the vane. Relative velocity of inlet to the vane is obtained by subtracting vectorially the velocity of the vane with its absolute velocity. It happens in the same way for V_r2. Thus, If the friction is neglected, then V_r1= V_r2.

8. Drag force is directly proportional to ________
a) Density of fluid
b) Mass density
c) Area
d) Flow speed
Answer: a
Clarification: Drag force is directly proportional to density of the fluid. It is the force that acts opposite to the relative motion of any object moving with respect to its surroundings. Thus, the correct option is ‘a’.

9. Drag force can exist between two layers of liquid.
a) True
b) False
Answer: a
Clarification: Drag force can exist between two layers of liquid. They can even exist in between two layers of solid surface. Unlike other resistive forces, they are dependent on velocity.

10. The efficiency of the vane is given by_________
a) 1-V₂² / V₁²
b) 1-(V₂² / V₁²)
c) V₂² / V₁²
d) 1- V₁²
Answer: a
Clarification: In a velocity triangle at the inlet and the outlet, the control volume is moving with a uniform velocity. Therefore, the momentum theorem of the control volume is at a steady flow. Thus, the efficiency of the vane is given by 1-(V₂² / V₁²).

11. Drag coefficient is a function of _________
a) Mach number
b) Froude’s number
c) Laminar flow
d) Reynolds number
Answer: a
Clarification: Drag coefficient is a function of Mach number. In fluid dynamics, the drag coefficient has no dimensions. It is a dimensionless quantity. Drag coefficient is used to quantify the resistance of an object in a fluid environment.

12. For a streamlined body to achieve low drag coefficient, the boundary layer must_________
a) Flow over the body
b) Be attached to the body
c) Move away from the body
d) Move parallel to the body
Answer: b
Clarification: For a streamlined body to achieve low drag coefficient, the boundary layer must be attached to the surface of the body for a long time as possible. This causes the wake to be narrow.

13. There will be a transition from laminar flow to turbulent flow when______
a) Reynolds number increases
b) Reynolds number decreases
c) Reynolds number is the same
d) Froude’s number increases
Answer: a
Clarification: There will be a transition from laminar flow to turbulent flow with the increase in the Reynolds number. Reynolds number below 2000 is laminar flow and Reynolds number above 2000 is for turbulent flow.

14. With the increase in flow velocity, Reynolds number_________
a) Increases
b) Decreases
c) Same
d) Independent
Answer: a
Clarification: With the increase in flow velocity, Reynolds number increases. Reynolds number below 2000 is laminar flow and Reynolds number above 2000 is for turbulent flow. Thus, the correct option is Increases.

15. With the decrease in the viscosity, Reynolds number ________
a) Increases
b) Decreases
c) Same
d) Independent
Answer: a
Clarification: With the decrease in viscosity, Reynolds number increases. Reynolds number below 2000 is laminar flow and Reynolds number above 2000 is for turbulent flow. Thus, the correct option is Increases.

Fluid Mechanics Multiple Choice Questions on “Most Economic Rectangular Section”.

1. For a channel to be economic which of the following parameters should be minimum.
a) Wetted perimeter
b) Wetted area
c) Section factor
d) Hydraulic depth
Answer: a
Clarification: If the wetted perimeter is minimum, amount of materials required for construction of the channel is less and hence the channel is more economical.

2. A rectangular channel section has depth y and width B, calculate the most economical area of the channel.
a) 2y²
b) y²
c) By
d) B²
Answer: a
Clarification:

3. The depth and widths of a rectangular channel section are y and B respectively, determine the economical perimeter of the section.
a) y
b) 2y
c) 3y
d) 4y
Answer: d
Clarification:

Fluid Mechanics Interview Questions and Answers for freshers on “Thermodynamic Properties, Compressibility and Bulk Modulus”.

1. If there is no exchange of heat between system and surrounding where system comprises of a compressible fluid but the heat is generated due to friction, the process is an adiabatic.
a) True
b) False
Answer: b
Clarification: For process to be adiabatic, there is no heat exchange and no heat generation within fluid.

2. For a compressible fluid, if there is no change in specific volume at constant temperature, what type of process it is?
a) Isothermal process
b) Adiabatic Process
c) Polytropic process
d) None of the mentioned
Answer:a
Clarification: As, specific volume remains constant, density remains constant. Therefore for given temperature there is no change in volume. hence, the process is isothermal.

3. If the fluid is incompressible, do thermodynamic properties play an important role in its behaviour at varying temperature and pressure?
a) Yes
b) No
c) Depends on the fluid
d) None of the mentioned
Answer: b
Clarification: If fluid is incompressible there is not much change in observed properties with variation in temperature and pressure. Hence, no perceivable change.

4. If for same temperature and pressure change, the value of bulk modulus is compared for isothermal process and adiabatic process, which one would be higher?
a) Isothermal process
b) Adiabatic process
c) Value is constant for both the processes
d) None of the mentioned
Answer: b
Clarification: For isothermal process
K=p
For adiabatic process
K=kp
where K=Bulk modulus
k=Polytropic constant
p=Pressure.

5. The value of gas constant is same for all the gases
a) True
b) False
Answer: b
Clarification: The value of gas constant depends on molecular weight. As the molecular weight is different, gas constant will be different.

6. Calculate the pressure exerted by 9 kg of air at a temperature of 20℃ if the volume is 0.8m3. Assuming ideal gas laws are applicable.
a) 946 kN/m²
b) 1892 kN/m²
c) 1419 kN/m²
d) None of the mentioned
Answer: a
Clarification: Ideal gas Law: PV=nRT
n=M/m
P=(9*8314*293)/28.97=946 kN/m².

7. A gas weighs 16 N/m3 at 30℃ and at an absolute pressure of 0.35 N/mm². Determine the gas constant.
a) 708.23
b) 354.11
c) 531.17
d) 1062.34
Answer:a
Clarification: R=P/(ρ*T)=3500000*9.81/16*303=708.23.

8. A cylinder of 0.8 m3 in volume contains superheated steam at 70℃ and .4 N/m² absolute pressure. The superheated steam is compressed to .3 . Find pressure and temperature.
a) 0.74 N/m², 422.3℃
b) 1.48 N/m², 422.3℃
c) 0.74 N/m², 844.6℃
d) 1.48 N/m², 844.6℃
Answer: a
Clarification: For polytropic process,

P2=(v1/v2)n *P1
=(0.8/0.3)1.3 * 0.4 ……..(for superheated stream n=1.3)
=.74 N/m2
T1=P1v1/nR=422.3℃.

9. Determine the compressibility of an incompressible fluid, if the pressure of the fluid is changed from 70 N/m² to 130 N/m². The volume of the liquid changes by 0.15 percent.
a) 0.0025 m²/N
b) 0.0050 m²/N
c) 0.0070 m²/N
d) 0.0012 m²/N
Answer:a
Clarification: Compressibility=1/Bulk Modulus
=1/K
K=(dp*V/dv)
=60/0.15
=400
Compressibility=.0025.

10. What is the variation of cp, cv and k in case of gases when the temperature increases?
a) cp and cv decreases with temperature, and k increases
b) cp and cv increase with temperature, and k decreases
c) cp and cv increase with temperature, and k increases
d) cp and cv decreases with temperature, and k decreases
Answer:b
Clarification: cp is molar heat capacity at constant pressure. As temperature is increased, enthalpy increases, heat capacity increases.
Same is for cv, cp is molar heat capacity at constant volume.
However cp-cv=R and cp/cv = R
Hence, as cp, cv increases R decreases.

To practice all areas of Fluid Mechanics for Interviews,

Category: Fluid Mechanics Objective Questions

250+ TOP MCQs on Conditions of Equilibrium of a Floating and Submerged Bodies and Answers

250+ TOP MCQs on Classification of Orifice & Hydraulic Coefficients and Answers

250+ TOP MCQs on Pipes in Series and Answers

250+ TOP MCQs on Drag on a Sphere and Answers

250+ TOP MCQs on Most Economic Rectangular Section and Answers

250+ TOP MCQs on Thermodynamic Properties & Compressibility and Answers