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Multiple choice question for engineering

Set 1

1. What will be the shape of the pathline for an one-dimensional flow be like?
a) straight line
b) parabolic
c) hyperbolic
d) elliptical

View Answer

Answer: a [Reason:] A pathline is the path followed by a particle in motion. For an one-dimensional flow, the fluids move in only one dimension (say x). Hence the pathline will also be a straight line (along that direction).

2. Which of the following is correct?
a) Pathlines of two particles in an one-dimensional flow can never intersect
b) Pathlines of two particles in an one-dimensional flow can never intersect if the two particles move along the same direction
c) Pathlines of two particles in an one-dimensional flow can intersect only if the two particles move along the same direction
d) Pathlines of two particles in an one-dimensional flow can intersect only if the two particles move along different directions

View Answer

Answer: c [Reason:] The pathline of a particle in an one-dimensional flow is a straight line along the direction it moves. If the two particles move along the same direction, their pathlines will be parallel to each other and will never intersect.

3. What is the maximum number of times the pathlines of two particles can intersect in an one dimensional flow?
a) 0
b) 1
c) 2
d) infinite

View Answer

Answer: b [Reason:] The pathline of a particle in an one-dimensional flow is a straight line along the direction it moves. When two particles move in the same direction, their pathline will never intersect and when they move in different directions, their pathlines will intersect only once.

4. The velocity of a point in a flow is
a) along the streamline
b) tangent to the streamline
c) along the pathline
d) tangent to the pathline

View Answer

Answer: b [Reason:] A pathline is the path followed by a particle in motion whereas a streamline is an imaginary line within the flow such that the tangent at any point on it indicates the velocity at that point.

5. Which of the following is correct?
a) A streamline can intersect itself and two streamlines can cross
b) A streamline cannot intersect itself but two streamlines can cross
c) A streamline can intersect itself but two streamlines cannot cross
d) A streamline cannot intersect itself and two streamlines cannot cross

View Answer

Answer: d [Reason:] A streamline is defined as an imaginary line within the flow such that the tangent at any point on it indicates the velocity at that point. At a point, there can only be one direction of velocity. Hence, neither can a streamline intersect itself nor can two streamlines cross each other.

6. If three sets of streamlines A, B and C are considered across section 1-2, which set will represent accelerated flow from 1 to 2?
fluid-mechanics-questions-answers-types-flow-lines-q3
a) A
b) B
c) C
d) None of the sets

View Answer

Answer: a [Reason:] Streamline spacing varies inversely as the velocity. Higher the velocity, closer will be the streamlines. Hence, converging of streamlines from 1 to 2 will indicate accelerated flow as in set A.

7. The streamlines of the particles in a flow are recorded. If the streamline distribution remain the same even after sometime, what type of flow can it be?
a) steady
b) unsteady
c) uniform
d) non-uniform

View Answer

Answer: a [Reason:] A streamline is defined as an imaginary line within the flow such that the tangent at any point on it indicates the velocity at that point. In a steady flow, the velocity of the particles is constant with time. Hence, the streamlines remain the same even after sometime.

8. If the streamlines of the particles in a flow are parallel to each other, what type of flow can it be?
a) steady
b) unsteady
c) uniform
d) non-uniform

View Answer

Answer: c [Reason:] Streamline spacing varies inversely as the velocity. In a uniform flow, the velocities of the particles are the same at every instant of time. Hence, the spacing between their streamlines will be the same. In other words, the streamlines will be parallel.

9. Which of the following is correct?
a) the movement of fluid mass can either be along the streamlines or across them
b) the movement of fluid mass can be along the streamlines but never across them
c) the movement of fluid mass can never be along the streamlines but can be across them
d) the movement of fluid mass can neither be along the streamlines or across them

View Answer

Answer: b [Reason:] A streamline is defined as an imaginary line within the flow such that the tangent at any point on it indicates the velocity at that point. Flow can only be along the velocity, never perpendicular to it. Hence, the movement of fluid mass can only be along the streamlines and never across them.

10. Which of the following is correct?
a) pathlines are concerned with a number of particles at the same instant and streamlines with a particular particle at successive instants of time
b) pathlines are concerned with a particular particle at successive instants of time and streamlines with a number of particles at the same instant
c) both pathlines and streamlines are concerned with a number of particles at the same instant
d) both pathlines and streamlines are concerned with a particular particle at successive instants of time

View Answer

Answer: b [Reason:] A pathline is the path followed by a particle in motion whereas a streamline is an imaginary line within the flow such that the tangent at any point on it indicates the velocity at that point. Thus, pathlines are concerned with a particular particle at successive instants of time and streamlines with a number of particles at the same instant.

11. The path taken by the smoke coming out of a chimney (in concentric circles) represents a
a) pathline
b) streamline
c) streakline
d) streamtube

View Answer

Answer: c [Reason:] A pathline is the path followed by a particle in motion whereas a streamline is an imaginary line within the flow such that the tangent at any point on it indicates the velocity at that point. A streamtube is a collection of streamlines. A streakline is a curve which gives an instantaneous picture of the location of the fluid particleswhich have passed through a given point. Hence, the path taken by the smoke coming out of a chimney (in concentric circles) will represent streaklines.

12. Which of the following is correct?
a) In steady flow, pathlines and streamlines are identical
b) In steady flow, pathlines and streaklines are identical
c) In steady flow, streaklines and streamlines are identical
d) In steady flow, pathline, streamlines and streaklines are all identical

View Answer

Answer: d [Reason:] In case of a steady flow, the velocity at a point remains constant with time. Thus, there will be no geometrical distinction between the pathlines, streamlines and streaklines.

13. Which of the following is correct?
a) There will be no flow across the streamtube
b) There will be no flow along the streamtube
c) There will be no flow both across the streamtube and along it
d) There will be flow both across the streamtube and along it

View Answer

Answer: a [Reason:] Streamtube is a fluid mass bounded by a group of streamlines. Since, the movement of the fluid mass can only be along the streamlines and never across them, there will be no flow across the streamtube.

Set 2

1. The relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d where A and n are constants. If n = 1, what type of fluid will it be?
a) Newtonian fluid
b) Non-Newtonian fluid
c) Pseudoplastic
d) Bingham plastic

View Answer

Answer: a [Reason:] When n = 1, the relation reduces to Newton’s law of viscosity: z = A * , where A will represent the viscosity of the fluid. The fluid following this relation will be a Newtonian fluid.

2. The relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d where A and n are constants. If n > 1, what type of fluid will it be?
a) Newtonian fluid
b) Dilatant
c) Pseudoplastic
d) Bingham plastic

View Answer

Answer: b [Reason:] When n ≠ 1, the relation will be treated as Power law for Non-Newtonian fluids: fluid-mechanics-questions-answers-types-fluid-q1d. For n > 1, the rate of change of the shear stress increases with the increase in the value of velocity gradient. Such fluids are called Dilatants.

3. The relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d where A and n are constants. If n < 1, what type of fluid will it be?
a) Newtonian fluid
b) Dilatant
c) Pseudoplastic
d) Bingham plastic

View Answer

Answer: c [Reason:] When n ≠ 1, the relation will be treated as Power law for Non-Newtonian fluids: fluid-mechanics-questions-answers-types-fluid-q1d. For n < 1, the rate of change of the shear stress decreases with the increase in the value of velocity gradient. Such fluids are called Pseudoplastics.

4. The relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d + B where A, n and B are constants. Which of the following conditions will hold for a Bingham plastic?
a) A = 0;B ≠ 0; n ≠ 1
b) A ≠ 0;B = 0; n ≠ 1
c) A = 0;B = 0; n = 1
d) A ≠ 0;B ≠ 0; n = 1

View Answer

Answer: d [Reason:] For Bingham Plastics, shear stress will not remain constant after an yield value of stress. Thus, A ≠ 0;B ≠ 0. After the yield value, the relation between the shear stress and velocity gradient will become linear. hus, n = 1.

5. The relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d+ B where A, n and B are constants. Which of the following conditions will hold for a Rheopectic?
a) A = 0;B ≠ 0; n > 1
b) A ≠ 0;B = 0; n < 1
c) A = 0;B = 0; n < 1
d) A ≠ 0;B ≠ 0; n > 1

View Answer

Answer: d [Reason:] For Rheopectics, shear stress will not remain constant after an yield value of stress. Thus, A ≠ 0; B ≠ 0. After the yield value, the rate of change of the shear stress increases with the increase in the value of velocity gradient. Thus, n > 1.

6. The relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d + B where A, n and B are constants. Which of the following conditions will hold for a Thixotropic fluid?
a) A = 0;B ≠ 0; n > 1
b) A ≠ 0;B = 0; n > 1
c) A = 0;B = 0; n < 1
d) A ≠ 0;B ≠ 0; n < 1

View Answer

Answer: d [Reason:] For Thixotropics, shear stress will not remain constant after an yield value of stress. Thus, A ≠ 0;B ≠ 0. After the yield value, the rate of change of the shear stress decreases with the increase in the value of velocity gradient. Thus, n < 1.

7. The graph shows relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d where A and n are constants. The graphs are drawn for three values of n. Which one will be the correct relationship between n1, n2 and n3?
fluid-mechanics-questions-answers-types-fluid-q7
a) n1 > n2 > n3
b) n1 < n2 < n3
c) n1 > n3 > n2
d) n1 < n3 < n2

View Answer

Answer: b [Reason:] The graph corresponding to n = n1 represents Pseudoplastics, for which the rate of change of the shear stress decreases with the increase in the value of velocity gradient. The graph corresponding to n = n2 represents Newtonian fluids, for which shear stress changes linearly with the change in velocity gradient. The graph corresponding to n = n3 represents Dilatents, for which the rate of change of the shear stress increases with the increase in the value of velocity gradient.

8. Which of the following is a shear-thinnning fluid?
a) Bingham plastic
b) Rheopectic
c) Dilatant
d) Pseudoplastic

View Answer

Answer: d [Reason:] Shear-thinning fluids are those which gets strained easily at high values of shear stresses. The relation between shear stress Z and velocity gradient of a shear-thinning fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d, where A and n are constants and n < 1. This relation is followed by Pseudoplastics.

9. Which of the following is a shear-thickening fluid?
a) Bingham plastic
b) Thixotropic
c) Dilatant
d) Pseudoplastic

View Answer

Answer: c [Reason:] Shear-thickening fluids are those for which it gets harger to strain it at high values of shear stresses. The relation between shear stress Z and velocity gradient of a shear-thickening fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d where A and n are constants and n > 1. This relation is followed by Dilatants.

10. For what value of flow behaviour index, does the consistency index has a dimension independent of time?
a) 0
b) 1
c) 2
d) 3

View Answer

Answer: c [Reason:] The relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d where A is the flow consistency index and n is the flow behaviour index. fluid-mechanics-questions-answers-types-fluid-q10 Thus [A] will be independent of time when n = 2.

11. What will be the dimension of the flow consistency index for a fluid with a flow behaviour index of 3?
a) [M L-2 T].
b) [M L-2 T-1].
c) [M L-1 T-2].
d) [M L-1 T].

View Answer

Answer: d [Reason:] The relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d where A is the flow consistency index and n is the flow behaviour index. Putting n = 3, fluid-mechanics-questions-answers-types-fluid-q11

12. What will be the dimension of the flow consistency index for a fluid with a flow behaviour index of -1?
a) N/m2 s2
b) N/m2 s
c) N/ms
d) N/ms2

View Answer

Answer: b [Reason:] The relation between shear stress Z and velocity gradient of a fluid is given by fluid-mechanics-questions-answers-types-fluid-q1d where A is the flow consistency index and n is the flow behaviour index. If n = -1, A = Z * Unit of Z is N/m2 and is s-1. Thus, the unit of A will be N/m2 s.

Set 3

1. Which method is used exclusively in fluid mechanics?
a) Lagrangian method
b) Eulerian method
c) Both Lagrangian and Eulerian methods
d) Neither Lagrangian nor Eulerian method

View Answer

Answer: b [Reason:] In Fluid Mechanics, the matter of concern is the general state of motion at various points in the fluid system (as in Eulerian approach) rather than the motion of each particle (as in Lagrangian approach). Hence, the Eulerian method is extensively used in Fluid Mechanics.

2. A beaker contains water up to a certain height as shown. If the water is allowed to get discharged through a small pipe (of a uniform diameter), what type of flow will it be in the pipe?
fluid-mechanics-questions-answers-types-fluid-flow-q2
a) steady and uniform
b) unsteady and uniform
c) steady and non-uniform
d) unsteady and non-uniform

View Answer

Answer: b [Reason:] The velocity in which the water is discharged with a velocity With time as the water gets discharged,v decreases as H decreases. Hence, it will be an unsteady flow. According to the continuity equation, ρAV =constant, where ρ= density, A= cross-sectional area of flow, V = velocity of flow. Since water is treated as an incompressible liquid (ρ =constant) and the pipe has a uniform diameter (A =constant) at a given instant, V will remain constant throughout the whole cross-section of the pipe. Hence, it will be a uniform flow.

3. A beaker contains water up to a certain height as shown. If the water is allowed to get discharged through a small nozzle, what type of flow will it be in the pipe?

a) steady and uniform
b) unsteady and uniform
c) steady and non-uniform
d) unsteady and non-uniform

View Answer

Answer: d [Reason:] The velocity in which the water is discharged with a velocity With time as the water gets discharged,v decreases as H decreases. Hence, it will be an unsteady flow. According to the continuity equation, ρAV =constant, where ρ= density, A= cross-sectional area of flow, V = velocity of flow. In this case, water is treated as an incompressible liquid (ρ = constant) but the nozzle has a gradually decreasing diameter (A decreases). At a given instant, V at the exit of the nozzle will be more than that at it’s entrance. Hence, it will be a non-uniform flow.

4. A beaker contains water up to a certain height as shown. If the water is allowed to get discharged through a small diffuser, what type of flow will it be in the pipe?

a) steady and uniform
b) unsteady and uniform
c) steady and non-uniform
d) unsteady and non-uniform

View Answer

Answer: d [Reason:] The velocity in which the water is discharged with a velocity With time as the water gets discharged,v decreases as H decreases. Hence, it will be an unsteady flow. According to the continuity equation, ρAV =constant, where ρ= density, A= cross-sectional area of flow, V = velocity of flow. In this case, water is treated as an incompressible liquid (ρ =constant) but the nozzle has a gradually increasing diameter (A increases). At a given instant, V at the exit of the nozzle will be less than that at it’s entrance. Hence, it will be a non-uniform flow.

5. What type of flow can be taken for granted in a pipe of a uniform cross-section?
a) steady
b) unsteady
c) uniform
d) non-uniform

View Answer

Answer: c [Reason:] According to the continuity equation, ρAV =constant, where ρ= density, A= cross-sectional area of flow, V = velocity of flow. For a pipe of a uniform cross-section, no matter what the rate of flow is, the velocity of flow inside the pipe will always remain constant. Hence, it’ll always be a uniform flow. It’ll be a steady flow if and only if the water level is maintained at a constant level by supplying water at the same rate as it gets discharged, else the water level will keep decreasing with time leading to an unsteady flow.

6. Can the flow inside a nozzle be steady and uniform?
a) yes
b) never
c) it can be steady but never uniform
d) it can be uniform but never steady

View Answer

Answer: c [Reason:] According to the continuity equation, ρAV =constant, where ρ= density, A= cross-sectional area of flow, V = velocity of flow. For a nozzle, the area gradually decreases towards it’s exit. Thus, no matter what the rate of flow is, the velocity of flow at the nozzle exit will always be greater than that at it’s entrance. Hence, it’ll always be an unsteady flow. It can be a steady flow if and only if the water level is maintained at a constant level by supplying water at the same rate as it gets discharged, else the water level will keep decreasing with time leading to an unsteady flow.

7. Which of the following statements is true regarding one and two-dimensional flows?
a) Flow in a pipe is always taken as one-dimensional flow
b) Flow in a pipe is always taken as two-dimensional flow
c) Flow in a pipe is taken as one-dimensional flow when average flow parameters are considered
d) Flow in a pipe is taken as two-dimensional flow when average flow parameters are considered

View Answer

Answer: c [Reason:] The flow inside a pipe can be described by the cylindrical co-ordinate system (r; θ; z), where r is in the radial direction, θ in the angular direction and z in the axial direction. For a circular cross-sections, the flow can be taken to be independent of θ. Hence, it can be taken aa a two-dimensional flow. Again if aerage flow parameters are considered to account for the variation in the radial direction, the flow can be taken as an one-dimensional flow.

8. Which of the following is true?
a) Flow is rotational inside the boundary layer and irrotational outside
b) Flow is irrotational inside the boundary layer and rotational outside
c) Flow is rotational both inside and outside of the boundary layer
d) Flow is irrotational both inside and outside of the boundary layer

View Answer

Answer: a [Reason:] When a torque is applied to a fluid particle, it undergoes a rotation. Thus, the rotation of a fluid particle will alwayds be associated with shear stress. Shear stress is in turn dependent on the viscosity. Hence, rotational flow occurs where the viscosity effects are predominant. Since, viscosity effects are predominant inside the blundary layer, the flow will be rotational in this region. However, outside the boundary layer, the viscosity effects are negligible. Hence, flow can be treated as irrotational outside the boundary layer.

9. Which of the following is true?
a) Flow is laminar inside the boundary layer and turbulent outside
b) Flow is turbulent inside the boundary layer and laminar outside
c) Flow is laminar both inside and outside of the boundary layer
d) Flow is turbulent both inside and outside of the boundary layer

View Answer

Answer: a [Reason:] Flows can be characterized as laminar or turbulent on the basis of Reynold’s number Re = ρvd / μ, where ρ is the density, d is the pipe diameter and μ is the viscosity. For Re < 2000, the flow will be laminar and Re > 4000, the ow will be turbulent. For laminar flow, the viscosity effects must be high (μ should be high) as inside the boundary layer. Outside the boundary layer, the viscosity effects are negligible. Hence, the flow will be turbulent.

10. “The velocity of entrance and exit through a nozzle remains the same.” Is this ever possible?
a) only if the flow is compressible
b) only if the flow is laminar
c) only if the flow is rotational
d) never possible

View Answer

Answer: a [Reason:] According to the continuity equation, ρAV =constant, where ρ= density, A= cross sectional area of flow, V = velocity of flow. If v =constant, ρA =constant. Thus a change is A will mean a change in ρ. Hence, the flow is possible only if the fluid is compressible.

11. Three flows named as 1,2 and 3 are observed. The Reynold’s number for the three are 100, 1000 and 10000. Which of the flows will be laminar?
a) only 1
b) only 1 and 2
c) 1, 2 and 3
d) only 3

View Answer

Answer: b [Reason:] Flows can be characterized as laminar or turbulent on the basis of Reynold’s number Re = ρvd / μ, where ρ is the density, d is the pipe diameter and μ is the viscosity. For Re < 2000, the flow will be laminar and Re > 4000, the flow will be turbulent. Thus, flow 1 and 2 will be laminar.

12. Three flows named as 1,2 and 3 are observed. The flow velocities are v1 and v2. If all other geometrical factors remain the same along with the fluid considered, flow is more likely to be laminar?
a) flow 1 if v1 > v2
b) flow 2 if v1 > v2
c) always flow 1
d) always flow 2

View Answer

Answer: [Reason:] Flows can be characterized as laminar or turbulent on the basis of Reynold’s number Re = ρvd / μ, where ρ is the density, d is the pipe diameter and μ is the viscosity. If all other geometrical factors remain the same along with the fluid considered, v1 > v2 implies Re1 > Re2. Thus, flow 2 is more likely to be laminar.

Set 4

1. When fluid element moves from one position to another, what type of motion is it?
a) Linear Translation
b) Linear Deformation
c) Angular Deformation
d) Rotation

View Answer

Answer: a [Reason:] As per the definition, bodily movement of fluid element is translation.

2. When fluid element moves from one position to another and it undergoes c hange in its dimensions, what type of motion is it?
a) Linear Translation
b) Linear Deformation
c) Angular Deformation
d) Rotation

View Answer

Answer: b [Reason:] As per the definition, bodily movement of fluid element causing it to change its dimension is linear deformation.

3. If there is change in angle contained by two sides. the average of the angle is
a) Linear Translation
b) Linear Deformation
c) Angular Deformation
d) Rotation

View Answer

Answer: c [Reason:] As per the definition, the sum average of two angles is magnitude of angular deformation.

4. What is the magnitude of vorticity?
a) Twice of angular rotation
b) Thrice of angular rotation
c) Two and half times of angular rotation
d) Same as angular rotation

View Answer

Answer: a [Reason:] It is the mathematical relation between the two.

5. The flow of fluid along curvilinear or curved path is known as
a) Curvilinear Flow
b) Circular Flow
c) Sink Flow
d) Vortex Flow

View Answer

Answer: d [Reason:] The flow of fluid along curvilinear or curved path is known as Vortex flow.

6. When external torque is absent the type of vortex flow is
a) Circular vortex flow
b) Independent vortex flow
c) Free vortex flow
d) None of the mentioned

View Answer

Answer: c [Reason:] Free vortex flow is due to the absence of any external force.

7. Which of the following is not an example of forced vortex flow?
a) Liquid contained in cylinder rotated about its axis
b) Flow of liquid inside impeller of a centrifugal pump
c) Flow of a water through runner of a turbine
d) Flow of the liquid around a circular bend in a pipe

View Answer

Answer: d [Reason:] Flow of the liquid around a circular bend in a pipe is an example of free vortex flow.

8. Which of the following is not an example of free vortex flow?
a) Flow of a water through runner of a turbine
b) Flow of liquid through a hole provided at the bottom
c) A whirlpool in a river
d) Flow of the liquid around a circular bend in a pipe

View Answer

Answer: a [Reason:] Flow of a water through runner of a turbine is an example of forced vortex flow.

9. Equation of motion for vortex flow does not take into account centrifugal force?
a) True
b) False

View Answer

Answer: b [Reason:] Equation of motion for vortex flow does take into account centrifugal force.

10. Equation of motion for vortex flow does take into account shear force
a) True
b) False

View Answer

Answer: b [Reason:] Equation of motion for vortex flow does not take into account shear force.

Set 5

1. Which of the following statement is true about vapor pressure of a liquid?
a) Vapor pressure is closely related to molecular activity and temperature of the liquid
b) Vapor pressure is closely related to molecular activity but independent of the temperature of the liquid
c) Vapor pressure is not affected by molecular activity and temperature of the liquid
d) Vapor pressure is not affected by molecular activity and is independent of the temperature of the liquid

View Answer

Answer: a [Reason:] The vapor pressure of a liquid at a given temperature is given by the pressure ex-erted by the saturated vapor on the liquid surface. When the vapor is saturated, an equilibrium exists between the liquid and the vapor phases. The number of molecules leaving the liquid surface is equal to the number of molecules entering the liquid surface. Hence, it is obvious that vapor pressure will be related to molecular activity and consequently to temperature. With the increase in temperature molecular activity increases as a result of which vapor pressure increases.

2. Which of the following equation correctly depicts the relation between the vapor pressure of a liquid and it’s temperature?
a) Vapor pressure increases linearly with the increase in temperature of the liquid
b) Vapor pressure increases slightly with the increase in temperature of the liquid at low temperatures and the rate of increase goes high at higher temperatures
c) Vapor pressure increases rapidly with the increase in temperature of the liquid at low temperatures and the rate of increase goes low at higher temperatures
d) Vapor pressure remains unchanged with the increase in temperature of the liquid

View Answer

Answer: b [Reason:] Vapor pressure is closely related to molecular activity which is in turn dependant on the temperature of the liquid. With the increase in temperature molecular activity of a vapor increases slowly at first and then rapidly. Similar is the nature of variaion of vapor pressure.

3. Which of the following is the condition for the boiling of a liquid?
a) Absolute pressure of a liquid must be greater than or equal to it’s vapor pressure
b) Absolute pressure of a liquid must be less than or equal to it’s vapor pressure
c) Absolute pressure of a liquid must be equal to it’s vapor pressure
d) Absolute pressure of a liquid must be greater than it’s vapor pressure

View Answer

Answer: b [Reason:] As the absolute pressure of a liquid goes below it’s vapor pressure, the formation of vapor bubbles start. Thus, for boiling to start, the absolute pressure of a liquid must be less than or equal to it’s vapor pressure.

4. Which of the following machines have the possibility of cavitation?
a) Reaction turbines and centrifugal pumps
b) Reaction turbines and reciprocating pumps
c) Impulse turbines and centrifugal pumps
d) Impulse turbines and reciprocating pumps

View Answer

Answer: a [Reason:] Cavitation occurs whenever absolute pressure of a liquid drops below it’s vapor pressure. Dropping of pressure is observed mainly in reaction turbines and centrifugal pumps.

5. The three liquids 1, 2, and 3 with vapor pressures V1, V2 and V3 respectively, are kept under same pressure. If V1 > V2 > V3, which liquid will start boiling early?
a) liquid 1
b) liquid 2
c) liquid 3
d) they will start boiling at the same time

View Answer

Answer: a [Reason:] A liquid starts to boil whenever it’s absolute pressure drops below it’s vapor pressure. Thus, the absolute pressure of liquid 1 will drop early, as a result it’ll start boiling early.

6. Equal amount of a particular liquid is poured into three similar containers, namely 1, 2 and 3, at a temperature of T1, T2 and T3 respectively. If T1 < T2 < T3, the liquid in which container will have the highest vapor pressure?
a) container 1
b) container 2
c) container 3
d) the vapor pressure of the liquid will remain the same irrespective of it’s temperature

View Answer

Answer: c [Reason:] Higher the temperature, higher is the molecular activity and consequently, higher is the vapor pressure of a given liquid. Since, container 3 is at the highest temperature, liquid in it will have the highest vapor pressure.

7. The absolute pressure of a water is 0.5kN above it’s vapor pressure. If it flows with a velocity of 1m/s, what will be the value of Cavitation Number describing the flow induced boiling?
a) 0.25
b) 0.5
c) 1
d) 2

View Answer

Answer: c [Reason:] fluid-mechanics-questions-answers-vapor-pressure-q7

8. Which of the following is correct regarding the formation and collapse of vapor bubbles in a liquid?
a) Vapor bubbles are formed when the fluid pressure goes above the vapor pressure and collapses when the fluid pressure goes above the bubble pressure
b) Vapor bubbles are formed when the fluid pressure goes above the vapor pressure and collapses when the fluid pressure goes below the bubble pressure
c) Vapor bubbles are formed when the fluid pressure drops below the vapor pressure and collapses when the fluid pressure goes below the bubble pressure
d) Vapor bubbles are formed when the fluid pressure drops below the vapor pressure and collapses when the fluid pressure goes above the bubble pressure

View Answer

Answer: d [Reason:] Whenever the absolute pressure of a fluid drops below it’s vapor pressure, bubble formation starts. Again, when the fluid pressure goes above the bubble pressure, it’ll collapse. This is how cavitation formation takes place.