Fluid Mechanics MCQs

Multiple Choice Questions 33 Pages

Savitribai Phule Pune University

Civil Engineering

RBJ

Contributed by

Raju Bhai Johal

Unit I a) Fluid Flow around Submerged Objects
1. Whenever a plate is held immersed at some angle with the direction of flow of the liquid,
it is subjected to some pressure. The component of this pressure, in the direction of flow
of the liquid, is known as
A. Lift
B. Drag
C. Stagnation pressure
D. Bulk modulus
Answer: Option B
2. The region between the separation of streamline and boundary surface of the solid body
is known as
A. Wake
B. Drag
C. Lift
D. Boundary layer
Answer: Option A
3. Whenever a plate is held immersed at some angle with the direction of flow of the liquid,
it is subjected to some pressure. The component of this pressure, at right angles to the
direction of flow of the liquid is known as …
A. Wake
B. Drag
C. Lift
D. Boundary layer
Answer: Option C
4. Drag is defined as the force exerted by a flowing fluid on a solid body
A. in the direction of flow
B. perpendicular to the direction of flow
C. in the direction which is at an angle of 45
0
to the direction of flow.
D. none of the above.
Answer: Option A
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5. Lift force is defined as the force exerted by a flowing fluid on a solid body
A. in the direction of flow
B. perpendicular to the direction of flow
C. in the direction which is at an angle of 45
0
to the direction of flow.
D. none of the above.
Answer: Option B
6. Drag force (F
D
) is expressed mathematically, as
A.
2
1
2
D D
F V C A


B.
2
D D
F V C A


C.
2
2
D D
F V C A


D. none of the above.
Answer: Option A
7. Lift force (F
L
) is expressed mathematically, as
A.
2
1
2
L L
F V C


B.
2
1
2
L L
F V C A


C.
2
2
L L
F V C A


D.
2
L L
F V C A


.
Answer: Option B
8. Total drag on body is the sum of
A. pressure drag and velocity drag
B. pressure drag and friction drag
C. friction drag and velocity drag
D. none of the above.
Answer: Option B
9. A body is called stream lined body when it is placed in a flow and the surface of the body
A. coincides with streamlines
B. does not coincide with streamlines
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C. is perpendicular to the streamlines
D. none of the above.
Answer: Option A
10. A body is called bluff body if the surface of the body
A. coincides with streamlines
B. does not coincide with streamlines
C. is very smooth
D. none of the above.
Answer: Option B
11. The drag on the sphere (F
D
) for Reynolds’s number less than 0.2 is given by
A.
5
D
F DU


B.
D
F DU


C.
2
D
F DU


D.
3
D
F DU


.
Answer: Option D
12. The skin friction drag on the sphere (for Reynolds’s number less than 0.2) is equal to
A. one third of the total drag
B. half of the total drag
C. two third of the total drag
D. None of the above.
Answer: Option C
13. The pressure drag on the sphere (for Reynolds’s number less than 0.2) is equal to
A. one third of the total drag
B. half of the total drag
C. two third of the total drag
D. None of the above.
Answer: Option A
14. The terminal fall velocity of falling body is equal to
A. a maximum velocity with which body will fall
B. a maximum constant velocity with which body will fall
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C. half of the maximum velocity
D. none of the above.
Answer: Option B
15. When a falling body has attained terminal velocity, the weight of the body is equal to
A. drag force minus buoyant force
B. buoyant force minus drag force
C. drag force plus the buoyant force
D. none of the above.
Answer: Option C
16. The tangential velocity of ideal fluid at any point on the surface of the cylinder is given
by
A.
1
sin
2
u U



B.
sin
u U



C.
2 sin
u U




D. none of the above.
Answer: Option C
17. The Lift force (F
L
) produced on a rotating circular cylinder in a uniform flow is given
by…(where L = length of the cylinder, U= Free stream velocity, Г= Circulation).
A.
L
LU
F



B.
L
F LU

 
C.
L
U
F





D.
L
LU
F



.
Answer: Option B
18. The lift co-efficient (C
L
) for a rotating circular cylinder in a uniform flow is given by…
(where R = Radius of the cylinder, U= Free stream velocity, Г= Circulation).
A.
L
U
C
R


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B.
L
R
C
U


C.
L
C
RU



D.
L
RU
C


.
Answer: Option C
19. The pressure drag depends upon
A. the characteristics of the oncoming flow
B. the boundary formation
C. the separation of boundary layer and the size of the wake
D. the shear stresses generated on the body surface.
Answer: Option C
20. In case of airfoils, the profile drag is one which is caused by
A. the compressibility effects
B. the shape and orientation of airfoil
C. the circulation induced around aerofoil
D. none of the above.
Answer: Option B
21. A flat plate 1.5 m x 1.5 m moves at 50 km/hr in stationary air of density 1.15 kg/m
3
. If
the co-efficient of drag and lift are 0.15 and 0.75 respectively, determine lift force and
choose the correct answer from the following
A. 150.23 N
B. 178.60 N
C. 108.85 N
D. 187.20 N.
Answer: Option D
22. A flat plate 1.5 m x 1.5 m moves at 50 km/hr in stationary air of density 1.15 kg/m
3
. If
the co-efficient of drag and lift are 0.15 and 0.75 respectively, determine drag force and
choose the correct answer from the following
A. 50.23 N
B. 78.60 N
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C. 37.44 N
D. 87.20 N.
Answer: Option C
23. A flat plate 1.5 m x 1.5 m moves at 50 km/hr in stationary air of density 1.15 kg/m
3
. If
the drag and lift force are 37.44 N and 187.20 N respectively, determine the resultant
force and choose the correct answer from the following
A. 160.23 N
B. 178.60 N
C. 137.44 N
D. 190.85 N.
Answer: Option D
24. A flat plate 1.5 m x 1.5 m moves at 50 km/hr in stationary air of density 1.15 kg/m
3
. If
the drag and lift force are 37.44 N and 187.20 N respectively, determine the power
required to keep the plate in motion in kW and choose the correct answer from the
following
A. 0.519
B. 0.456
C. 0.789
D. 0.528 .
Answer: Option A
25. A flat plate 2 m x 2 m moving at a speed of 4 m/s normal to its plane in water, determine
the drag force in N and choose the correct answer from the following
A. 36800
B. 35800
C. 36750
D. 36000 .
Answer: Option A
26. A flat plate 2 m x 2 m moving at a speed of 4 m/s normal to its plane in air of density
1.24 kg/m
3
, determine the drag force in N and choose the correct answer from the
following
A. 36.80
B. 35.80
C. 45.60
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D. 36.00.
Answer: Option C
27. A metallic ball of diameter 2x10
-3
m drops in a fluid of sp. gr. 0.95 and viscosity 15
Poise. The density of metallic ball is 12000 kg/m
3
. Determine the drag force in N exerted
by fluid on metallic ball.
A. 0.000459
B. 0.000454
C. 0.000786
D. 0.000108.
Answer: Option B
28. A metallic ball of diameter 2x10
-3
m drops in a fluid of sp. gr. 0.95 and viscosity 15
Poise. The density of metallic ball is 12000 kg/m
3
. If drag force is 0.000454 N exerted by
fluid on metallic ball, find the pressure drag and skin friction drag.
A. 0.0001513 N and 0.0003028 N
B. 0.0001613 N and 0.0003328 N
C. 0.0001583 N and 0.0003928 N
D. 0.0001583 N and 0.0003828 N.
Answer: Option A
29. A metallic ball of diameter 2x10
-3
m drops in a fluid of sp. gr. 0.95 and viscosity 15
Poise. The density of metallic ball is 12000 kg/m
3
. If drag force is 0.000454 N exerted by
fluid on metallic ball, find terminal fall velocity.
A. 0.019
B. 0.007
C. 0.016
D. 0.018.
Answer: Option C
30. A metallic ball of diameter 2x10
-3
m drops in a fluid of sp. gr. 0.95 and viscosity 15
Poise. The density of metallic ball is 12000 kg/m
3
. If the maximum constant velocity of
falling metallic ball is 0.016 m/s, find the Reynolds number.
A. 100
B. 7
C. 10.756
D. 0.02.
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Answer: Option D.
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Unit III a) Uniform Flow
Q.1 If Velocity, pressure, density etc., do not change at a point with respect to time, flow is called
a) Uniform
b) Incompressible
c) Non-Uniform

d) Steady
Ans: d
Q.2 If velocity, pressure, density etc., change at a point with respect to time, flow is called
a) Uniform
b) Compressible
c) Unsteady
d) Incompressible
Ans: c
Q.3 If the velocity in a fluid flow does not change with respect to length of direction of flow, it is called
a) Steady flow
b) Uniform flow
c) Incompressible
d) Rotational
Ans: b
Q.4 If the velocity in a fluid flow change with respect to length of direction of flow, it is called
a) Unsteady flow
b) Compressible flow
c) Irrotational flow
d) None of the above
Ans: d
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Q.5 If the density of the fluid is constant from point to point in a flow region, it is called
a) Steady flow.
b) Incompressible Flow
c) Uniform flow
d) Rotational flow.
Ans: b
Q.6 If the density of the flow changes from point to point in a flow region, it is called
a) Steady flow.
b) Unsteady flow
c) Non uniform
d) compressible
Ans: d
Q.7 Chezy’s Formula is given as
a) V= S√(RC)
b) V= C √(RS)
c) V= R √(CS)
d) None of the above.
Ans: b
Q.8 The discharge through the rectangular channel is maximum when
a) R= d/3
b) R= d/2
c) R= 2d
d) R= 3d/2
Where, R= hydraulic mean depth, d= depth of the flow
Ans: b
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Fluid Mechanics MCQs

Fluid Mechanics MCQs

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