Important Objective Questions On Fluid Machines
1.Centre of buoyancy always
coincides with the centre of gravity
coincides with the centroid of the volume of fluid displaced
remains above the centre of gravity
remains below the centre of gravity
ANSWER : : coincides with the centroid of the volume of fluid displaced
2.An open cubical tank of 2 m side is filled with water. If the tank is rotated with an acceleration such that half of the water spills out, then the acceleration is equal to
g/3
g/2
2g/3
g
ANSWER : : g
3.When a liquid rotates at a constant angular velocity about a vertical axis as a rigid body, the pressure intensity varies
linearly with radial distance
as the square of the radial distance
inversely as the square of the radial distance
inversely as the radial distance
ANSWER : : as the square of the radial distance
4.The unit of kinematic viscosity is
gm/cm-sec2
dyne-sec/cm2
gm/cm2-sec
cm2/sec
ANSWER : : cm2/sec
5.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
0.25
0.50
1.0
none of the above
ANSWER : : 1.0
6.An ideal fluid is
one which obeys Newton’s law of viscosity
frictionless and incompressible
very viscous
frictionless and compressible
ANSWER : : frictionless and incompressible
7.Metacentric height for small values of angle of heel is the distance between the
centre of gravity and centre of buoy-ancy
centre of gravity and metacentre
centre of buoyancy and metacentre
free surface and centre of buoyancy
ANSWER : : centre of gravity and metacentre
8.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 ?
(i) and (ii)
(i)and(iv)
(ii) and (iii)
(iii) and (iv)
ANSWER : : (i)and(iv)
9.The position of center of pressure on a plane surface immersed vertically in a static mass of fluid is
at the centroid of the submerged area
always above the centroid of the area
always below the centroid of the area
none of the above
ANSWER : : always below the centroid of the area
10.The eddy viscosity for turbulent flow is
a function of temperature only
a physical property of the fluid.
dependent on the flow
independent of the flow
ANSWER : : dependent on the flow
11.If the weight of a body immersed in a fluid exceeds the buoyant force, then the body will
rise until its weight equals the buoyant force
tend to move downward and it may finally sink
float
none of the above
ANSWER : : tend to move downward and it may finally sink
12.The viscosity of a gas
decreases with increase in temperature
increases with increase in temperature
is independent of temperature
is independent of pressure for very high pressure intensities
ANSWER : : increases with increase in temperature
13.A floating body is said to be in a state of stable equilibrium
when its metacentric height is zero
when the metacentre is above the centre of gravity
when the metacentre is below the centre of gravity
only when its centre of gravity is below its centre of buoyancy
ANSWER : : when the metacentre is above the centre of gravity
14.Flow at constant rate through a tapering pipe is i) steady flow ii) uniform flow iii) unsteady flow iv) non-uniform flow The correct answer is
(i) and (ii)
(i)and(iv)
(ii) and (iii)
(ii) and (iv)
ANSWER : : (i)and(iv)
15.If a vessel containing liquid moves downward with a constant acceleration equal to ‘g’ then
the pressure throughout the liquid mass is atmospheric
there will be vacuum in the liquid
the pressure in the liquid mass is greater than hydrostatic pressure
none of the above
ANSWER : : the pressure throughout the liquid mass is atmospheric
16.The increase in meta centric height i) increases stability ii) decreases stability iii) increases comfort for passengers iv) decreases comfort for passengers The correct answer is
(i) and (iii)
(i)and(iv)
(ii) and (iii)
(ii) and (iv)
ANSWER : : (i)and(iv)
17.The point in the immersed body through which the resultant pressure of the liquid may be taken to act is known as
center of gravity
center of buoyancy
center of pressure
metacentre
ANSWER : : center of pressure
18.The total pressure on a plane surface inclined at an angle 9 with the horizontal is equal to
PA
pA sin 9
pA cos 9
pA tan 9
ANSWER : re p is pressure intensity at centroid of area and A is area of plane surface.
19.An open tank contains 1 m deep water with 50 cm depth of oil of specific gravity 0.8 above it. The intensity of pressure at the bottom of tank will be
4 kN/m2
10 kN/m2
12 kN/m2
14 kN/m2
ANSWER : : 14 kN/m2
20.A rectangular block 2 m long, 1 m wide and 1 m deep floats in water, the depth of immersion being 0.5 m. If water weighs 10 kN/m3, then the weight of the block is
5kN
lOkN
15 kN
20 kN
ANSWER : : lOkN
16.The increase in meta centric height i) increases stability ii) decreases stability iii) increases comfort for passengers iv) decreases comfort for passengers The correct answer is
(i) and (iii)
(i)and(iv)
(ii) and (iii)
(ii) and (iv)
ANSWER : : (i)and(iv)
17.The point in the immersed body through which the resultant pressure of the liquid may be taken to act is known as
center of gravity
center of buoyancy
center of pressure
metacentre
ANSWER : : center of pressure
18.The total pressure on a plane surface inclined at an angle 9 with the horizontal is equal to
PA
pA sin 9
pA cos 9
pA tan 9
ANSWER : re p is pressure intensity at centroid of area and A is area of plane surface.
19.An open tank contains 1 m deep water with 50 cm depth of oil of specific gravity 0.8 above it. The intensity of pressure at the bottom of tank will be
4 kN/m2
10 kN/m2
12 kN/m2
14 kN/m2
ANSWER : : 14 kN/m2
20.A rectangular block 2 m long, 1 m wide and 1 m deep floats in water, the depth of immersion being 0.5 m. If water weighs 10 kN/m3, then the weight of the block is
5kN
lOkN
15 kN
20 kN
ANSWER : : lOkN
21.Newton’s law of viscosity relates
intensity of pressure and rate of angular deformation
shear stress and rate of angular deformation
shear stress, viscosity and temperature
viscosity and rate of angular deformation
ANSWER : : shear stress and rate of angular deformation
22.A vertical rectangular plane surface is submerged in water such that its top and bottom surfaces are 1.5 m and 6.0 m res-pectively below the free surface. The position of center of pressure below the free surface will be at a distance of
3.75 m
4.0 m
4.2m
4.5m
ANSWER : : 4.2m
23.The horizontal component of force on a curved surface is equal to the
product of pressure intensity at its centroid and area
force on a vertical projection of the curved surface
weight of liquid vertically above the curved surface
force on the horizontal projection of the curved surface
ANSWER : : force on a vertical projection of the curved surface
24.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 center of bottom is
zero
one-fourth its value when cylinder was full
one-half its value when cylinder was full
cannot be predicted from the given data
ANSWER : : zero
25.The pressure at the summit of a syphon is
equal to atmospheric
less than atmospheric
more than atmospheric
none of the above
ANSWER : : less than atmospheric
26.If the velocity is zero over half of the cross-sectional area and is uniform over the remaining half, then the momentum correction factor is
1
4/3
2
4
ANSWER : : 2
27.The discharge through a V- notch varies as
H1/2
H3’2
H5/2
H5’4 where H is head.
ANSWER : : H5/2
28.In a forced vortex motion, the velocity of flow is
directly proportional to its radial distance from axis of rotation
inversely proportional to its radial distance from the axis of rotation
inversely proportional to the square of its radial distance from the axis of rotation
directly proportional to the square of its radial distance from the axis of rotation
ANSWER : : directly proportional to its radial distance from axis of rotation
29.Stream lines and path lines always coincide in case of
steady flow
laminar flow
uniform flow
turbulent flow
ANSWER : : steady flow
30.The continuity equation pi V,A,= p2V2A2 is based on the following assumption regarding flow of fluid
steady flow
uniform flow
incompressible flow
frictionless flow
ANSWER : re pi and p2 are mass densities.
31.Which of the following is an incorrect statement ?
Coefficient of contraction of a venturimeter is unity.
Flow nozzle is cheaper than venturimeter but has higher energy loss.
Discharge is independent of orientation of venturimeter whether it is horizontal, vertical or inclined.
None of the above statement is correct.
ANSWER : : None of the above statement is correct.
32.Which of the following is used to measure the discharge ?
current meter
venturimeter
pitot tube
hotwire anemometer
ANSWER : : venturimeter
33.Equation of continuity is based on the principle of conservation of
mass
energy
momentum
none of the above
ANSWER : : mass
34.Coefficient of velocity of venturimeter
is independent of Reynolds number
decreases with higher Reynolds number
is equal to the coefficient of discharge of venturimeter
none of the above
ANSWER : : is equal to the coefficient of discharge of venturimeter
35.The motion of air mass in a tornado is a
free vortex motion
forced vortex motion
free vortex at center and forced vortex outside
forced vortex at center and free vortex outside
ANSWER : : forced vortex at center and free vortex outside
36.In steady flow of a fluid, the total accele ration of any fluid particle
can be zero
is never zero
is always zero
is independent of coordinates
ANSWER : : can be zero
37.If velocity is zero over l/3rd of a cross-section and is uniform over remaining 2/3rd of the cross-section, then the correction factor for kinetic energy is
4/3
3/2
9/4
27/8
ANSWER : : 9/4
38.The theoretical value of coefficient of contraction of a sharp edged orifice is
0.611
0.85
0.98
1.00
ANSWER : : 0.611
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
(i) and (iii)
(ii) and (iii)
(i) and (iv)
(ii) and (iv)
ANSWER : : (ii) and (iv)
40.Hot wire anemometer is used to measure
discharge
velocity of gas
pressure intensity of gas
pressure intensity of liquid
ANSWER : : velocity of gas
41.The pitot tube is used to measure
velocity at stagnation point
stagnation pressure
static pressure
dynamic pressure
ANSWER : : stagnation pressure
42.Ay between two stream lines represents
velocity
discharge
head
pressure
ANSWER : : discharge
43.When the velocity distribution is uniform over the cross-section, the correction factor for momentum is
0
1
4/3
2
ANSWER : : 1
44.Coefficient of velocity for Borda’s mouth piece running full is
0.611
0.707
0.855
1.00
ANSWER : : 0.707
45.Which of the following velocity potentials satisfies continuity equation ?
x2y
x2-y2
cosx
x2 + y2
ANSWER : : x2-y2
46.Size of a venturimeter is specified by
pipe diameter
throat diameter
angle of diverging section
both pipe diameter as well as throat diameter
ANSWER : : pipe diameter
47.Due to each end contraction, the discharge of rectangular sharp crested weir is reduced by
5%
10%
15%
20%
ANSWER : : 5%
48.Select the incorrect statement.
The pressure intensity at vena contracta is atmospheric.
Contraction is least at vena contracta.
Stream lines are parallel throughout the jet at vena contracta.
Coefficient of contraction is always less than one.
ANSWER : : Stream lines are parallel throughout the jet at vena contracta.
49.The major loss of energy in long pipes is due to
sudden enlargement
sudden contraction
gradual contraction or enlargement
friction
ANSWER : : friction
50.Separation of flow occurs when
the pressure intensity reaches a minimum
the cross-section of a channel is reduced
the boundary layer comes to rest
all of the above
ANSWER : : the boundary layer comes to rest
51.Which of the following statements is correct?
Lower critical Reynolds number is of no practical significance in pipe flow problems.
Upper critical Reynolds number is significant in pipe flow problems.
Lower critical Reynolds number has the value 2000 in pipe flow
Upper critical Reynolds number is the number at which turbulent flow changes to laminar flow.
ANSWER : : Lower critical Reynolds number is of no practical significance in pipe flow problems.
52.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
0.423 D
0.577 D
0.223 D
0.707 D
ANSWER : re D is the depth of flow.
53.The distance y from pipe boundary, at which the point velocity is equal to average velocity for turbulent flow, is
0.223 R
0.423 R
0.577 R
0.707 R
ANSWER : re R is radius of pipe.
54.The value of friction factor ‘f’ for smooth pipes for Reynolds number 106 is approximately equal to
0.1
0.01
0.001
0.0001
ANSWER : : 0.01
55.The discharge over a broad crested weir is maximum when the depth of flow is
H/3
H/2
2 H/5
2 H/3
ANSWER : re H is the available head.
56.Coefficient of contraction for an external cylindrical mouthpiece is
1.00
0.855
0.7H
0.611
ANSWER : : 1.00
57.The ratio of average velocity to maximum velocity for steady laminar flow in circular pipes is
1/2
2/3
3/2
2
ANSWER : : 1/2
58.The distance from pipe boundary, at which the turbulent shear stress is one-third die wall shear stress, is
1/3 R
1/2 R
2/3 R
3/4R
ANSWER : re R is the radius of pipe.
59.For a sphere of radius 15 cm moving with a uniform velocity of 2 m/sec through a liquid of specific gravity 0.9 and dynamic viscosity 0.8 poise, the Reynolds number will be
300
337.5
600
675
ANSWER : : 675
60.The shear stress distribution for a fluid flowing in between the parallel plates, both at rest, is
constant over the cross section
parabolic distribution across the section
zero at the mid plane and varies linearly with distance from mid plane
zero at plates and increases linearly to midpoint
ANSWER : : zero at the mid plane and varies linearly with distance from mid plane
61.For hydro-dynamically smooth boundary, the friction coefficient for turbulent flow is
constant
dependent only on Reynolds number
a function of Reynolds number and relative roughness
dependent on relative roughness only
ANSWER : : dependent only on Reynolds number
62.When an ideal fluid flows past a sphere,
highest intensity of pressure occurs around the circumference at right angles to flow
lowest pressure intensity occurs at front stagnation point
lowest pressure intensity occurs at rear stagnation point
total drag is zero
ANSWER : : total drag is zero
63.The boundary layer thickness in turbulent flow varies as
x”7
x,/2
x4/5
x3/5
ANSWER : re x is the distance from leading edge.
64.For laminar flow in a pipe of circular cross-section, the Darcy’s friction factor f is
directly proportional to Reynolds number and independent of pipe wall roughness
directly proportional to pipe wall roughness and independent of Reynolds number
inversely proportional to Reynolds number and indpendent of pipe wall roughness
inversely proportional to Reynolds number and directly proportional to pipe wall roughness
ANSWER : : inversely proportional to Reynolds number and indpendent of pipe wall roughness
65.In which of the following the friction drag is generally larger than pressure drag?
a circular disc or plate held normal to flow
a sphere
a cylinder
an airfoil
ANSWER : : an airfoil
66.Stanton diagram is a
log-log plot of friction factor against Reynolds number
log-log plot of relative roughness against Reynolds number
semi-log plot of friction factor against Reynolds number
semi-log plot of friction factor against relative roughness
ANSWER : : log-log plot of friction factor against Reynolds number
67.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
less than 1
between 1 and 100
160
200
ANSWER : : 160
68.Which of the following has highest coefficient of discharge ?
sharp edged orifice
venturimeter
Borda’s mouthpiece running full
CipoUetti weir
ANSWER : : venturimeter
69.In case of an airfoil, the separation of flow occurs
at the extreme rear of body
at the extreme front of body
midway between rear and front of body
any where between rear and front of body depending upon Reynolds number
ANSWER : : at the extreme rear of body
70.In a Sutro weir, the discharge is proportional to
H1/2
H3/2
H5/2
H
ANSWER : re H is head.
71.With the same cross-sectional area and immersed in same turbulent flow, the largest total drag will be on
a circular disc of plate held normal to flow
a sphere
a cylinder
a streamlined body
ANSWER : : a circular disc of plate held normal to flow
72.If x is the distance from leading edge, then the boundary layer thickness in laminar flow varies as
x
x
x
x/7
ANSWER : : x
73.Select the correct statement.
The absolute roughness of a pipe de-creases with time.
A pipe becomes smooth after using for long time.
The friction factor decreases with time.
The absolute roughness increases with time.
ANSWER : : The absolute roughness increases with time.
74.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
0.40 cm
0.20 cm
0.10 cm
0.05 cm
ANSWER : ume that boundary layer is entirely laminar.
75.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
1 m
10m
100m
none of the above
ANSWER : : 100m
76.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
from reservoir A to reservoirs B and C
from reservoir B to reservoirs C and A
from reservoir C to reservoirs A and B
unpredictable
ANSWER : : from reservoir C to reservoirs A and B
77.The speed of a pressure wave through a pipe depends upon
the length of pipe
the viscosity of fluid
the bulk modulus for the fluid
the original head
ANSWER : : the bulk modulus for the fluid
78.For laminar flow in circular pipes, the Darcy’s friction factor f is equal to
16/Re
32/ Re
64/ Re
none of the above where R,, is Reynolds number.
ANSWER : : 64/ Re
79Drag force is a function of i) projected area of the body ii) mass density of the fluid iii) velocity of the body The correct answer is
(i) and (ii)
(i) and (iii)
(ii) and (iii)
(i), (ii) and (iii)
ANSWER : : (i), (ii) and (iii)
80.Surge wave in a rectangular channel is an example of i) steady flow ii) unsteady flow iii) uniform flow iv) non-uniform flow The correct answer is
(i) and (iii)
(ii) and (iii)
(i) and (:v)
(ii) and (iv)
ANSWER : : (ii) and (iv)
81.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
less than d
between d and 1.5 d
between 1.5 d and 2d
greater than 2d
ANSWER : : less than d
82.The wake
always occurs before a separation point
always occurs after a separation point
is a region of high pressure intensity
none of the above
ANSWER : : always occurs after a separation point
83.The length of a pipe is 1 km and its diameter is 20 cm. If the diameter of an equivalent pipe is 40 cm, then its length is
32 km
20 km
8 km
4 km
ANSWER : : 32 km
84.In series-pipe problems
the head loss is same through each pipe
the discharge is same through each pipe
a trial solution is not necessary
the discharge through each pipe is added to obtain total discharge
ANSWER : : the discharge is same through each pipe
85.The maximum thickness of boundary layer in a pipe of radius r is
0
r/2
r
2r
ANSWER : : r
86.A fluid of kinematic viscosity 0.4 cm2/sec flows through a 8 cm diameter pipe. The maximum velocity for laminar flow will be
less than 1 m/sec
1 m/sec
1.5 m/sec
2 m/sec
ANSWER : : 1 m/sec
87.Two pipe systems are said to be equivalent when
head loss and discharge are same in two systems
length of pipe and discharge are same in two systems
friction factor and length are same in two systems
length and diameter are same in two systems
ANSWER : : head loss and discharge are same in two systems
88.The Prartdtl mixing length is
zero at the pipe wall
maximum at the pipe wall
independent of shear stress
none of the above
ANSWER : : zero at the pipe wall
89.The correct relationship among displacement thickness d, momentum thickness m and energy thickness e is
d > m > e
d > e > m
e > m > d
e > d > m
ANSWER : : e > d > m
90.The hydraulic grade line is
always above the centre line of pipe
never above the energy grade line
always sloping downward in the direction of flow
all of the above
ANSWER : : never above the energy grade line
91.The losses are more in
laminar flow
transition flow
turbulent flow
critical flow
ANSWER : : turbulent flow
92.The horse power transmitted through a pipe is maximum when the ratio of loss of head due to friction and total head supplied is
1/3
1/4
1/2
2/3
ANSWER : : 1/3
93.The velocity distribution for laminar flow through a circular tube
is constant over the cross-section
varies linearly from zero at walls to maximum at centre
varies parabolically with maximum at the centre
none of the above
ANSWER : : varies parabolically with maximum at the centre
94.When time of closure tc = L/v0 (where L is length of pipe and v0 is speed of pressure wave), the portion of pipe length subjected to maximum head is
L/4
L/3
L/2
L
ANSWER : : L/4