# Fluid Mechanics Multiple choice Questions & Answers

Posted On:February 2, 2019, Posted By: Latest Interview Questions, Views: 1207, Rating :     ## Best Fluid Mechanics Objective Questions and Answers

Dear Readers, Welcome to Fluid Mechanics Objective Questions have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of Fluid Mechanics MCQs. These objective type Fluid Mechanics questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular question during your Job interview and these model questions are asked in the online technical test and interview of many IT & Non IT Industries.

### 1. Pascal-second is the unit of

a) pressure

b) kinematic viscosity

c) dynamic viscosity

d) surface tension

Ans: c ### 2. An ideal fluid is

a) one which obeys Newton's law of viscosity

b) frictionless and incompressible

c) very viscous

d) frictionless and compressible

Ans: b

a) gm/cm-sec2

b) dyne-sec/cm2

c) gm/cm2-sec

d) cm2/sec

Ans: d

### 4. If the dynamic viscosity of a fluid is 0.5 poise and specific gravity is 0.5, then the kinematic viscosity of that fluid in stokes is

a) 0.25

b) 0.50

c) 1.0

d) none of the above

Ans: c

### 5.     The viscosity of a gas

a) decreases with increase in temperature

b) increases with increase in temperature

c) is independent of temperature

d) is independent of pressure for very high pressure intensities

Ans: b

### 6.       Newton's law of viscosity relates

a)               intensity of pressure and rate of angular deformation

b) shear stress and rate of angular de¬formation

c) shear stress, viscosity and tempe¬rature

d) viscosity and rate of angular defor¬mation

Ans: b

a) 4 kN/m2

b) 10 kN/m2

c) 12 kN/m2

d) 14 kN/m2

Ans: d

### 17. The position of centre of pressure on a plane surface immersed vertically in a static mass of fluid is

a) at the centroid of the submerged area

b) always above the centroid of the area

c) always below the centroid of the area

d) none of the above

Ans: c

### 19.     The total pressure on a plane surface inclined at an angle 9 with the horizontal is equal to

a) PA

b) pA sin 9

c) pA cos 9

d) pA tan 9

where p is pressure intensity at centroid of area and A is area of plane surface.

Ans: a

a) 3.75 m

b) 4.0 m

c) 4.2m

d) 4.5m

Ans: c

### 21. Centre of buoyancy always

a) coincides with the centre of gravity

b) coincides with the centroid of the volume of fluid displaced

c) remains above the centre of gravity

d) remains below the centre of gravity

Ans: b

### 22. If the weight of a body immersed in a fluid exceeds the buoyant force, then the body will

a) rise until its weight equals the buoyant force

b) tend to move downward and it may finally sink

c) float

d) none of the above

Ans: b

### 23. Metacentric height for small values of angle of heel is the distance between the

a) centre of gravity and centre of buoy-ancy

b) centre of gravity and metacentre

c) centre of buoyancy and metacentre

d) free surface and centre of buoyancy

Ans: b

### 24. A floating body is said to be in a state of stable equilibrium

a) when its metacentric height is zero

b) when the metacentre is above the centre of gravity

c) when the metacentre is below the centre of gravity

d) only when its centre of gravity is below its centre of buoyancy

Ans: b

### 25.   The increase in metacentric height

i)    increases stability

ii)   decreases stability

iii)  increases comfort for passengers

iv)  decreases comfort for passengers

a)    (i) and (iii)

b) (i)and(iv)

c) (ii) and (iii)

d) (ii) and (iv)

Ans: b

a) 5kN

b) lOkN

c) 15 kN

d) 20 kN

Ans: b

### 27. The point in the immersed body through which the resultant pressure of the liquid may be taken to act is known as

a) centre of gravity

b) centre of buoyancy

c) centre of pressure

d) metacentre

Ans: c

### 28. If a vessel containing liquid moves downward with a constant acceleration equal to 'g' then

a) the  pressure  throughout the  liquid mass is atmospheric

b) there will be vacuum in the liquid

c) the pressure in the liquid mass is greater than hydrostatic pressure

d) none of the above

Ans: a

### 29. When a liquid rotates at a constant angular velocity about a vertical axis as a rigid body, the pressure intensity varies

b) as the square of the radial distance

c) inversely as the square of the radial distance

d) inversely as the radial distance

Ans: b

a) g/3

b) g/2

c) 2g/3

d) g

Ans: d

### 31. A right circular cylinder open at the top is filled with liquid and rotated about its vertical axis at such a speed that half the liquid spills out, then the pressure intensity at the centre of bottom is

a) zero

b) one-fourth  its  value when  cylinder was full

c) one-half its value when cylinder was full

d) cannot be predicted from the given data

Ans: a

### 32. The horizontal component of force on a curved surface is equal to the

a) product of pressure intensity at its centroid and area

b) force on a vertical projection of the curved surface

c) weight of liquid vertically above the curved surface

d) force on the horizontal projection of the curved surface

Ans: b

### 33. A closed tank containing water is moving in a horizontal direction along a straight line at a constant speed. The tank also contains a steel ball and a bubble of air. If the tank is decelerated horizontally, then

i)    the ball will move to the front

ii)   the bubble will move to the front

iii)  the ball will move to the rear

iv)  the bubble will move to the rear Find out which of the above statements are correct ?

a) (i) and (ii)

b) (i)and(iv)

c) (ii) and (iii)

d) (iii) and (iv)

Ans: b

### 34. The eddy viscosity for turbulent flow is

a) a function of temperature only

b) a physical property of the fluid.

c) dependent on the flow

d) independent of the flow

Ans: c

### 35. Flow at constant rate through a tapering pipe is

ii) uniform flow

iv) non-uniform flow

a) (i) and (ii)

b) (i)and(iv)

c) (ii) and (iii)

d) (ii) and (iv)

Ans: b

a) 22.5 m/sec.

b) 33 m/sec.

c) 40 m/sec.

d) 90 m/sec.

Ans: c

a) 0

b) 1

c) 4/3

d) 2

Ans: b

### 39. Least possible value of correction factor for

i) kinetic energy is zero

ii) kinetic energy is 1

iii) momentum is zero

iv) momentum is 1

The correct statements are

a) (i) and (iii)

b) (ii) and (iii)

c) (i) and (iv)

d) (ii) and (iv)

Ans: d

a) 1

b) 4/3

c) 2

d) 4

Ans: c

a) 4/3

b) 3/2

c) 9/4

d) 27/8

Ans: c

### pi V,A,= p2V2A2 is  based  on  the  following  assumption regarding flow of fluid

b) uniform flow

c) incompressible flow

d) frictionless flow

where pi and p2 are mass densities.

Ans: a

a) x2y

b) x2-y2

c) cosx

d) x2 + y2

Ans: b

### 46.     The motion of air mass in a tornado is a

a) free vortex motion

b) forced vortex motion

c) free vortex at centre and forced vortex outside

d) forced vortex at centre and free vortex outside

Ans: d

### 47.     In a forced vortex motion, the velocity of flow is

a) directly proportional to its radial distance from axis of rotation

b) inversely proportional to its radial distance from the axis of rotation

c) inversely proportional to the square of its radial distance from the axis of rotation

d) directly proportional to the square of its radial distance from the axis of rotation

Ans: a

### 48. Stream lines and path lines always coincide in case of

b) laminar flow

c) uniform flow

d) turbulent flow

Ans: a

### 51.     Equation of continuity is based on the principle of conservation of

a) mass

b) energy

c) momentum

d) none of the above

Ans: a

### 52. In steady flow of a fluid, the total accele ration of any fluid particle

a) can be zero

b) is never zero

c) is always zero

d) is independent of coordinates

Ans: a

### 53. The pitot tube is used to measure

a) velocity at stagnation point

b) stagnation pressure

c) static pressure

d) dynamic pressure

Ans: b

### 54. Hot wire anemometer is used to measure

a) discharge

b) velocity of gas

c) pressure intensity of gas

d) pressure intensity of liquid

Ans: b

a) 0.611

b) 0.85

c) 0.98

d) 1.00

Ans: a

### 56. Which of the following is used to measure the discharge ?

a) current meter

b) venturimeter

c) pitot tube

d) hotwire anemometer

Ans: b

### 60. Select the incorrect statement.

a) The pressure intensity at vena contracta is atmospheric.

b) Contraction is least at vena contracta.

c) Stream lines are parallel throughout the jet at vena contracta.

d) Coefficient of contraction is always less than one.

Ans: c

### 61. Size of a venturimeter is specified by

a) pipe diameter

b) throat diameter

c) angle of diverging section

d) both pipe diameter as well as throat diameter

Ans: a

a) 5%

b) 10%

c) 15%

d) 20%

Ans: a

### 63. The discharge through a V- notch varies as

a) H1/2

b) H3'2

c) H5/2

d) H5'4 where H is head.

Ans: c

### 64. Which of the following is an incorrect statement ?

a) Coefficient of contraction of a venturimeter is unity.

b) Flow nozzle is cheaper than venturimeter but has higher energy loss.

c) Discharge is independent of orientation of venturimeter whether it is horizontal, vertical or inclined.

d)              None of the above statement is correct.

Ans: d

### 65.   Coefficient of velocity of venturimeter

a) is independent of Reynolds number

b) decreases with higher Reynolds number

c) is equal to the coefficient of discharge of venturimeter

d) none of the above

Ans: c

### 66. The pressure at the summit of a syphon is

a) equal to atmospheric

b) less than atmospheric

c) more than atmospheric

d) none of the above

Ans: b

a) velocity

b) discharge

d) pressure

Ans: b

a) 0.611

b) 0.707

c) 0.855

d) 1.00

Ans: b

a) slightly less

b) slightly more

c) nearly half

d) equal

Ans: a

### 70. The major loss of energy in long pipes is due to

a) sudden enlargement

b) sudden contraction

d) friction

Ans: d

a) 1.00

b) 0.855

c) 0.7H

d) 0.611

Ans: a

### 72. Which of the following has highest coefficient of discharge ?

a)     sharp edged orifice

b) venturimeter

c) Borda's mouthpiece running full

d) CipoUetti weir

Ans: b

a) H1/2

b) H3/2

c) H5/2

d) H

Ans: d

### 74. The discharge over a broad crested weir is maximum when the depth of flow is

a) H/3

b) H/2

c) 2 H/5

d) 2 H/3

where H is the available head.

Ans: d

### 78. Which of the following statements is correct?

a) Lower critical Reynolds number is of no practical significance in pipe flow problems.

b) Upper critical Reynolds number is significant in pipe flow problems.

c) Lower critical Reynolds number has the value 2000 in pipe flow

d) Upper critical Reynolds number is the number at which turbulent flow changes to laminar flow.

Ans: a

a) 300

b) 337.5

c) 600

d) 675

Ans: d

### 80. The shear stress distribution for a fluid flowing in between the parallel plates, both at rest, is

a) constant over the cross section

b) parabolic distribution across the section

c) zero at the mid plane and varies linearly with distance from mid plane

d) zero at plates and increases linearly to midpoint

Ans: c

a) x

b) x

c) x

d) x/7

Ans: a

### 82. Stanton diagram is a

a) log-log plot of friction factor against Reynolds number

b) log-log plot of relative roughness against Reynolds number

c) semi-log plot of friction factor against Reynolds number

d) semi-log plot of friction factor against relative roughness

Ans: a

### 83. The depth 'd' below the free surface at which the point velocity is equal to the average velocity of flow for a uniform laminar flow with a free surface, will be

a) 0.423 D

b) 0.577 D

c) 0.223 D

d) 0.707 D

where D is the depth of flow.

Ans: b

### 84. The boundary layer thickness in turbulent flow varies as

a) x"7

b) x,/2

c) x4/5

d) x3/5

where x is the distance from leading edge.

Ans: c

### 85. The distance y from pipe boundary, at which the point velocity is equal to average velocity for turbulent flow, is

a) 0.223 R

b) 0.423 R

c) 0.577 R

d) 0.707 R

where R is radius of pipe.

Ans: a

### 86. If a sphere of diameter 1 cm falls in castor oil of kinematic viscosity 10 stokes, with a terminal velocity of 1.5 cm/sec, the coefficient of drag on the sphere is

a) less than 1

b) between 1 and 100

c) 160

d) 200

Ans: c

### 87. In case of an airfoil, the separation of flow occurs

a) at the extreme rear of body

b) at the extreme front of body

c) midway between rear and front of body

d) any where between rear and front of body depending upon Reynolds number

Ans: a

### 88.     When an ideal fluid flows past a sphere,

a) highest intensity of pressure occurs around the circumference at right angles to flow

b) lowest pressure intensity occurs at front stagnation point

c) lowest pressure intensity occurs at rear stagnation point

d) total drag is zero

Ans: d

### 89. With the same cross-sectional area and immersed in same turbulent flow, the largest total drag will be on

a) a circular disc of plate held normal to flow

b) a sphere

c) a cylinder

d) a streamlined body

Ans: a

### 90. In which of the following the friction drag is generally larger than pressure drag?

a) a circular disc or plate held normal to flow

b) a sphere

c) a cylinder

d) an airfoil

Ans: d

### 91. For hydro-dynamically smooth boundary, the friction coefficient for turbulent flow is

a) constant

b) dependent only on Reynolds number

c) a function of Reynolds number and relative roughness

d) dependent on relative roughness only

Ans: b

a) 0.1

b) 0.01

c) 0.001

d) 0.0001

Ans: b

### 93. For laminar flow in a pipe of circular cross-section, the Darcy's friction factor f is

a) directly proportional to Reynolds number and independent of pipe wall roughness

b) directly proportional to pipe wall roughness and independent of Reynolds number

c) inversely proportional to Reynolds number and indpendent of pipe wall roughness

d) inversely proportional to Reynolds number and directly proportional to pipe wall roughness

Ans: c

### 94. Separation of flow occurs when

a) the pressure intensity reaches a minimum

b) the cross-section of a channel is reduced

c) the boundary layer comes to rest

d) all of the above

Ans: c

a) 1/2

b) 2/3

c) 3/2

d) 2

Ans: a

### 97. The distance from pipe boundary, at which the turbulent shear stress is one-third die wall shear stress, is

a) 1/3 R

b) 1/2 R

c) 2/3 R

d) 3/4R

where R is the radius of pipe.

Ans: a

### 98. The discharge of a liquid of kinematic viscosity 4 cm2/sec through a 8 cm dia-meter pipe is 3200n cm7sec. The type of flow expected is

a) laminar flow

b) transition flow

c) turbulent flow

d) not predictable from the given data

Ans: a

### 99. The Prartdtl mixing length is

a) zero at the pipe wall

b) maximum at the pipe wall

c) independent of shear stress

d) none of the above

Ans: a

### 100. The velocity distribution for laminar flow through a circular tube

a) is constant over the cross-section

b) varies linearly from zero at walls to maximum at centre

c) varies parabolically with maximum at the centre

d) none of the above

Ans: c

### 101. A fluid of kinematic viscosity 0.4 cm2/sec flows through a 8 cm diameter pipe. The maximum velocity for laminar flow will be

a) less than 1 m/sec

b) 1 m/sec

c) 1.5 m/sec

d) 2 m/sec

Ans: b

### 102. The losses are more in

a) laminar flow

b) transition flow

c) turbulent flow

d) critical flow

Ans: c

### 103. The wake

a) always occurs before a separation point

b) always occurs after a separation point

c) is a region of high pressure intensity

d) none of the above

Ans: b

a) 0

b) r/2

c) r

d) 2r

Ans: c

### 105. The hydraulic grade line is

a) always above the centre line of pipe

b) never above the energy grade line

c) always sloping downward in the direction of flow

d) all of the above

Ans: b

### 106. Two pipe systems are said to be equivalent when

a)    head loss and discharge are same in two systems

b) length of pipe and discharge are same in two systems

c) friction factor and length are same in two systems

d) length and diameter are same in two systems

Ans: a

### 107.   In series-pipe problems

a) the head loss is same through each pipe

b) the discharge is same through each pipe

c) a trial solution is not necessary

d) the discharge through each pipe is added to obtain total discharge

Ans: b

### 108.    Select the correct statement.

a) The absolute roughness of a pipe de-creases with time.

b) A pipe becomes smooth after using for long time.

c) The  friction  factor  decreases  with time.

d) The   absolute   roughness   increases with time.

Ans: d

### 109. A valve is suddenly closed in a water main in wl.ich the velocity is 1 m/sec and velocity of pressure wave is 981 m/ sec. The inertia head at the valve will be

a) 1 m

b) 10m

c) 100m

d) none of the above

Ans: c

### 110. The speed of a pressure wave through a pipe depends upon

a) the length of pipe

b) the viscosity of fluid

c) the bulk modulus for the fluid

Ans: c

a) L/4

b) L/3

c) L/2

d) L

Ans: a

### 113. If the elevation of hydraulic grade line at the junction of three pipes is above the elevation of reservoirs B and C and below reservoir A, then the direction of flow will be

a) from reservoir A to reservoirs B and C

b) from reservoir B to reservoirs C and A

c) from reservoir C to reservoirs A and B

d) unpredictable

Ans: c

a) 32 km

b) 20 km

c) 8 km

d) 4 km

Ans: a

### 116. Two pipes of same length and diameters d and 2d respectively are connected in series. The diameter of an equivalent pipe of same length is

a) less than d

b) between d and 1.5 d

c) between 1.5 d and 2d

d) greater than 2d

Ans: a

a) 1/3

b) 1/4

c) 1/2

d) 2/3

Ans: a

### 118. The boundary layer thickness at a distance of l m from the leading edge of a flat plate, kept at zero angle of incidence to the flow direction, is O.l cm. The velocity outside the boundary layer is 25 ml sec. The boundary layer thickness at a distance of 4 m is

a) 0.40 cm

b) 0.20 cm

c) 0.10 cm

d) 0.05 cm

Assume that boundary  layer is entirely laminar.

Ans: b

### 119. Drag force is a function of

i) projected area of the body

ii) mass density of the fluid

iii) velocity of the body

a) (i) and (ii)

b) (i) and (iii)

c) (ii) and (iii)

d) (i), (ii) and (iii)

Ans: d

a) d > m > e

b) d > e > m

c) e > m > d

d) e > d > m

Ans: d

### 121. For laminar flow in circular pipes, the Darcy's friction factor f is equal to

a) 16/Re

b) 32/ Re

c) 64/ Re

d) none of the above where R,, is Reynolds number.

Ans: c

### 122. Surge wave in a rectangular channel is an example of

iii) uniform flow

iv) non-uniform flow

a) (i) and (iii)

b) (ii) and (iii)

c) (i) and (:v)

d) (ii) and (iv)

Ans: d

### 123. The best hydraulic channel cross-section is the one which has a

a) minimum roughness coefficient

b) least cost

c) maximum area for a given flow

d) minimum wetted perimeter

Ans:

a) rectangle

b) triangle

c) trapezoidal

d) semi-circle

Ans:

### 125. Hydraulic jump is a

ii) uniform flow

iv) non-uniform flow

a) (i) and (ii)

b) (i) and (iv)

c) (ii) and (iii)

d) (iii) and (iv)

Ans:

### 126. The hydraulic jump always occurs from

a) below critical depth to above critical depth

b) above critical depth to below critical depth

c) below critical depth to above normal depth

d) above normal depth to below normal depth

Ans:

### 127. In a gradually varied flow

a) the slopes of energy grade line, hydraulic grade line and bottom of the channel are same

b) the slopes of energy grade line and hydraulic grade line are same but slope of the bottom of channel is different

c) the slopes of hydraulic grade line and bottom of channel are same but slope of energy grade line is different

d) the slope of energy grade line, hydraulic grade line and bottom of channel are all different.

Ans:

### 128. The flow in channels is considered to be in transitional state if the Reynolds number is

a) less than 500

b) between 500 and 2000

c) between 2000 and 4000

d) greater than 4000

Ans:

### 130. For shooting flow the Froude number is

a) zero

b) less than one

c) one

d) greater than one

Ans:

### 131. For uniform flow in a channel

a) the total energy line, water surface and bottom of channel are all horizontal

b) the total energy line and water surface are horizontal but bottom of channel is inclined

c) the total energy line, hydraulic gradient line and bottom of channel are all parallel

d) water surface and bottom of channel are parallel to each other but energy grade line is not parallel to them

Ans:

### 132. The Chezy's coefficient

a) is dimensionless

b) has the dimension of velocity

c) has the dimension of discharge

d) has the dimension Ll/2 T1

Ans:

a) venturi flume

b) current meter

c) pitot tube

d) all the above

Ans:

a) 0.50 m

b) 1.20 m

c) 2.50 m

d) 5.50 m

Ans:

a) 0

b) lm

c) 2m

d) 3m

Ans:

### 147. When the slope of bottom of a channel rises in the direction of flow, it is called

a) critical slope

b) mild slope

c) steep slope

Ans:

### 148. For any channel section, the specific energy increases with

i)    increase in depth of sub critical flow

ii)   increase in depth of super critical flow

iii) decrease in depth of sub critical flow

iv)  decrease in depth of super critical

a) (i) and (ii)

b) (i)and(iv)

c) (ii) and (iii)

d) (iii) and (iv)

Ans:

### 149. Flow through a venturi flume is maximum when the depth at the throat is

a) half

b) one-third

c) two-third

d) equal to the total energy of flow

Ans:

### 150. For the slope of bottom of a channel to be mild, the normal depth should be

a) greater than critical depth

b) equal to critical depth

c) less than critical depth

d) imaginary

Ans:

### 151. Super critical flow can occur in a

a) channel with a mild slope

b) channel with a steep slope

c) a horizontal channel

d) all the above

### 152. Analysis of a surge in open channels is carried but by using

i) Navier Stake's equation

ii) energy equation

iii) continuity equation

iv) momentum equation