Fluid mechanics MCQ-03

Q.1 The flow whose stream line may be re - presented by straight lines is called which type of flow ?

A. Uni directional flow

B. Two dimensional flow 

C. One dimensional flow

D. One directional flow 

Ans-: C

Q.2 Reynold's number for laminar flow is __.

A. 2000

B. More than 2000

C. Less than 2000

D. 1000

Ans-: C

Q.3 Reynold's number for turbulent flow is ______.

A. More than 10000

B. More than 4000

C. Less than 4000

D. 4000 

Ans-: B

Q.4 The transition from laminar to turbulent flow in a pipe depends on velocity , pipe diameter and kinematic viscosity of the fluid is known as which law?

A. Buoyancy law

B. Reynolds law

C. Avegadro law

D. Bernoulli law

Ans-: B

Q.5 The flow of liquid whoes stream line may be represented by the curve is called __.

A. Two dimensional flow 

B. Three dimensional flow

C. Two directional flow 

D. None of these 

Ans-: B

Q.6 laminar flow is also known as ____.

A. Uniform flow 

B. Steady flow 

C. Stream line flow 

D. Simple flow 

Ans-: C

Q.7 In laminar flow ____.

A. Liquid particles cross each other 

B. Liquid particles do not cross each other 

C. Liquid particles have constant velocity 

D. All of the above 

Ans-: B

Q.8 Dimensions of surface tension are ____.

A. M^1 L^0 T ^-2

B. M^2 L^1 T ^-1

C. M^1 L ^2 T^-2

D. M^-1 L ^2 T^2

Ans -: A

Q.9 Due to the property of _____ falling drop of water become sphere .

A. Adhesion 

B. Surface tension 

C. Cohesion

D. Temperature 

Ans-: B

Q.10 _____ is used in manometers because it provide longer column due to low density.

A. Methanol 

B. Mercury 

C. Water

D. Alcohol 

Ans -: D

Q.11 stoke is the unit of _____.

A. Viscosity 

B. Kinematic viscosity 

C. Specific viscosity 

D. Velocity if fluid 

Ans-: B

Q.12 The buoyancy force is depend on the __.

A. Viscosity of fluid 

B. Mass of liquid displaced 

C. Force of body

D. Pressure of water 

Ans-: B

Q.13 The speed of sound in a ideal gas varies directly as its ____.

A. Temperature 

B. Absolute temperature  

C. Pressure 

D. Density of gas

Ans-: B

Q.14 what is the average value of coefficient of the discharge?

A. 0.52

B. 0.62

C. 0.72

D. 0.27

Ans-: B

Q.15 whatis the average value of coefficient of the velocity?

A. 0.79

B. 0.97

C. 0.59

D. 0.12

Ans-: B

Different types of flow

The path followed by a liquid particle in motion, is called " path line ".

According to equation of continuity og liquid flows or fundamental equation of liquid flow,if an incompressible liquid flow con- tinuously through a pipe or channel, the discharge remains the same irrespective of the cross - section.

Laminar flow -: The flow in which path of the individual particles of liquid do not cross each other, is called stream line flow or " laminar flow " .Reynolds number is less than 2000 for laminar flow. 

Turbulent flow -: In this type of flow path of the individual particles cross each other and particles do not have a definite paths called turbulent flow. For turbulent flow Reynolds number is more than 4000.

Uniform flow -: In uniform flow the ve - locities of liquid particles at the all section of the pipe , channel are equal. This generally refers to flows in channel. 

Non-uniform flow -: The flow in which ve - locities,of liquid particles at all section of the pipe or channel are not equal is called " non- uniform flow " .

Steady flow -: In this type of flow, the quantity of liquid flowing per second is constant is called stream line flow. 

Unsteady flow-: The flow in which the quantity of liquid flowing per second is not constant is called " unsteady flow  ".

Stream line-: The imaginary line, tangent to which , at any point indicates the direction of the motion at the point , is called " stream line " .

Streak and potential line -: The line in which the instantaneous positions of all fluid particles which have passed through a given point , is called streak line .

And the line joining the points of equal potential on adjacent flow lines, is called the  " potential line or equipotential line " .

Fluid mechanics MCQ-02

Q.1  At 0° C surface tension of water is ___.

A. 47.16 dyn/cm

B. 71.31 dyn/cm 

C. 74.16dyn/cm

D. 60.71dyn/cm

Ans-: C

Q.2 The force per unit area exerted by water on the sides and bottom of it's container is called ?

A. Total pressure 

B. Water pressure 

C. Water force 

D. None of these 

Ans-: B

Q.3 In a closed system, water vaporises rapidly in regions where the pressure drops below the vapour pressure. This phe -nomenon is known as _______.

A. Cavitation 

B. Conservation

C. Vaporization 

D. All of the above 

Ans-: A

Q.4 which of the following is dimensionless?

A. Specific speed 

B. Specific volume 

C. Specific gravity 

D. Specific weight 

Ans-: C

Q.5 For water at 0° C value of mass density in kg sec^2 / m^4 is ____.

A. 1

B. 10

C. 100

D. 1000

Ans-: C

Q.6 Absolute pressure is equal to atmospheric pressure and ____ pressure. 

A. Gauge pressure 

B. Surrounding pressure 

C. Vacuum pressure 

D. None of these 

Ans-: A

Q.7 in which flow ,the velocitiesof liquid particles at all section of the pipe and channel are equal?

A. Constant flow

B. Uniform flow

C. Linear flow

D. Nin- uniform flow

Ans-: B

Q.8 The instantaneous position of all liquid particles which have passed through a given point is called ______.

A. Streak line

B. Non - streak line

C. Straight line 

D. None of these 

Ans-: A

Q.9 which device is used for measuring the rate of flow of liquid through a small channel. 

A. Notch

B. Venturimeter

C. Thermometer 

D. All of the above 

Ans-: A

Q.10 The flow in which the quantity of liquid flowing per second is constant is called ____.

A. Turbulent flow

B. Steady flow

C. Uniform flow 

D. Laminar flow 

Ans-: B

Q.11 In which law path of individual particles of liquid do not cross the each other is called ?

A. Stream line flow

B. Laminar flow 

C. Un-steady flow

D. A+B

Ans-: D

Q.12 The density of water is 1000 kg/m^3 at which temperature?

A. 0° C 

B. 4 ° C

C. 0 ° K

D. 237.16 K 

Ans-: B

Q.13 What us the unit of surface tension?

A. Newton / m^2

B. Newton/ m

C. Newton/ m^2

D. Newton m

Ans-: B

Q.14 For which flow , general energy equation holds ?

A. Steady flow 

B. Turbulent flow 

C. Non- uniform flow 

D. All of the above 

Ans-: C

Q.15 pitot tube us used for measurement of _______.

A. Pressure 

B. Temperature 

C. Velocity 

D. Viscosity 

Ans-: C

Fluid mechanics basic

Fluid  -: A fluid is a substance that is capable of flowing , conform to shape of containing vessel. It also deforms continuously when it issubjected to even a smallest shear stress.

An ideal fluid is frictionless and also it is incompressible .

Viscosity-:It is the property of fluid by virtue of which it offers resistance to shear. Viscosity is caused by cohesive for between molecules of liquid and by collision between molecules of gas .Viscosity is practically independent of pressure and depend upon temperature only .

Unit of viscosity " poise " or 1 gm /cm/ sec.

( 1 poise = 0.1 Ns/ m^2 )

Kinematic viscosity -: It is the ratio of dynamic or absolute viscosity and density. It's unit is stoke . Stoke is equal to 1cm^2/sec.

Newton's law of viscosity -: newton's law of viscosity state that shear stress  ( between  adjacent layer of fluid) is directly proportional to velocity gradient. 

Shear stress = 𝝁 du / dx

( 𝝁 = coefficient of viscosity Pa sec or Ns/ m^2)

du/dx is known as velocity gradient or rate of shear strain and it is zero for fluids at rest.                                                                                          Fluid following newton's law of the viscosity is known as Newtonian fluids and other non - Newtonian fluids. An ideal fluid offers no resistance to flow but real fluid does.

( viscosity is zero for ideal fluid but not for real fluid. )

Surface tension -:                                                                   Liquid molecules are attracted to each other by equal forces in all directions. On the surface they are subjected to an inward attraction which us not balanced by the outward attraction. This cause the liquid surface to seek a minimum possible area due to surface tension. 

Surface tension is also expressed as force per unit length . 

Fluid mechanics MCQ -01

Q.1 Viscosity is the property of _____.

A. Solid 

B. Liquid 

C. Gas 

D. Substance 

Ans-: B

Q.2The ratio of absolute or dynamic viscosity and the density is known as ___.

A. Viscosity ratio 

B. Kinematic Viscosity 

C. Absolute viscosity 

D. All of the above 

Ans -: B

Q.3 The law which satate that shear stress is proportional to du/ dx is called _____.

A. Newton's law

B. Fluid law

C. Avogadro's law 

D. NOT

Ans -: A

Q.4 what is expressed as force (F)  per unit length ?

A. Surface tension 

B. Force 

C. Adhesion 

D. Cohesion 

Ans-: A

Q.5 What is the meaning of capillarity of the water ?

A. The phenomenon of rising water in a tube of small diameter dipped in water.

B. The phenomenon of falling  water in a tube of small diameter dipped in water. 

C. The phenomenon of rising water in a tube of large diameter dipped in water. 

D. None of these 

Ans -: A

Q.6 The intensity of pressure at any point in a fluid at rest, is the same in all direction.

A. Pascal law

B. Charles law

C. Newton law

D. Boyle's law 

Ans -: A

Q.7 Gauge pressure is measured with re - ference to ______.

A. Atmospheric pressure 

B. Absolute pressure 

C. At zero temperature 

D. None of these 

Ans-: A

Q.8 Local atmospheric pressure is measured by which instrument ?

A. Thermometer 

B. Mercury barometer 

C. Aneroid barometer 

D. B + C 

Ans -: D

Q.9 Density of water is maximum at ____.

A. 0 ° C

B. 4 ° C

C. 0 ° K

D. 100 ° C

Ans-: B

Q.10 Property of fluid by which it's own molecular are attracted is called ____.

A. Viscosity 

B. Adhesion 

C. Cohesion 

D. Surface tension 

Ans-: C

Q.11 Fluid is a substance which offers no re - sistance to change of ___.

A. Shape 

B. Pressure 

C. Temperature 

D. Volume 

Ans -: A

Q.12 In-viscous and incompressible fluids is known as ______.

A. Real fluid 

B. Ideal fluid 

C. Viscous fluid 

D. Pure fluid 

Ans-: B

Q.13 Liquid are not affected by change in pressure and temperature.

A. Yes 

B. No

C. At 0° C

D. None of these 

Ans -: B

Q.14 Units of mass density is ?

A. Kg sec / m^4 

B. Kg / m^3

C. Kg / km

D. Kg sec ^2 / m ^4

Ans -: D

Q.15 why , mercury  does not wet the glass?

A. Because of viscosity 

B. Because of cohesion

C. Because of adhesion

D. Because of surface tension 

Ans-: B

Statement of various law's

1. First law of thermodynamics 

Statement -: For a closed system undergoing a cycle net heat transfer (∑Q) is always equal to the net work transfer (∑w).

[ ∑Q = ∑w ] ( valid for cycle)

First law of thermodynamics is nothing but conservation of energy .

dQ = dE + dW     dQ = heat suply

dE = internal energy  dW = Work done

 This is the first law of thermodynamics for closed system undergoing a process .

( reversible and irreversible)

dW = P . dV 

For reversible process - dQ = dE + P.dV

Statement- when kinatic energy and poten tial energy are neglected. 

Second law of thermodynamics-:First law of thermodynamics says that energy is constant. It does not give any direction for a perticular process .

Second law of thermodynamics given diection of process, the concept of entropy  , hence this also known as directional law .

Calcius statement -: It is impossible to transfer heat from lower temperature to higher temperature without any external input .

Concept of heat engine

Heat engine -: Heat engine is a device which converts part of heat into work , and also re-jected some amount of heat to the surroun-ding source and sink .

Source ----- E ------ sink 

(Q1=Qs)       |        ( Q2= Qr)

                  Work

Q1 = Q2 + w 

W = Q1 - Q2  ------ eq. 1

Efficiency = w / Q1 

Eff.  = Q1 - Q2 / Q1

Eff.  = 1 - ( Q2 / Q1 )

Eff.  = 1 - ( Qr / Qs )

* Relationship between coefficient of         heat pump and cop of refrigeration-:

Working between some temperature limits-

Cop ( heat pump)   =  Q1 / ( Q1 - Q2) 

Cop ( refrigeration)   Q2 / ( Q1 - Q2 )

=     Q1        ×    Q1 - Q2  

   Q1- Q2               Q2

Cop ( H.P.)     =  Q1 / Q2

Cop ( R.f.)

Cop ( H.P )  -  Cop ( R.f.) = 1

      Q1      -         Q2      = 1

 Q1- Q2        Q1 - Q2 

Q1  -  Q2     = 1 .

Q1  -  Q1