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fluid mechanics MCQs

Practise focused fluid mechanics questions with marked answers for exam preparation and subject revision.

fluid mechanics Mcqs
1. In a two dimensional incompressible steady flow around an airfoil, the stream lines are 2 cm apart at a great distance from the airfoil, where the velocity is 30 m/sec. The velocity near the airfoil, where the stream lines are 1.5 cm apart, is_________________?
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A. 90 m/sec

B. 22.5 m/sec

C. 40 m/sec

D. 33 m/sec

2. Which of the following is an incorrect statement ?
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A. Coefficient of contraction of a venturimeter is unity

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

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

D. None of the above statement is correct.
3. 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________________?
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A. less than d

B. between 1.5 d and 2d

C. greater than 2d

D. between d and 1.5 d

4. 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_________________?
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A. 600

B. 337.5

C. 300

D. 675
5. 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_____________________?
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A. 32 km

B. 8 km

C. 20 km

D. 4 km

6. Due to each end contraction, the discharge of rectangular sharp crested weir is reduced by________________?
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A. 10%

B. 15%

C. 20%

D. 5%
7. The horizontal component of force on a curved surface is equal to the_______________?
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A. weight of liquid vertically above the curved surface

B. force on a vertical projection of the curved surface

C. force on the horizontal projection of the curved surface

D. product of pressure intensity at its centroid and area

8. The ratio of average velocity to maximum velocity for steady laminar flow in circular pipes is_______________?
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A. 1/2

B. 2

C. 2-Mar

D. 3-Feb

9. 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__________________?
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A. 27/8

B. 3-Apr

C. 9/4

D. 2-Mar

10. The pressure at the summit of a syphon is_______________?
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A. equal to atmospheric

B. more than atmospheric

C. none of the above

D. less than atmospheric
11. Hot wire anemometer is used to measure_______________?
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A. pressure intensity of liquid

B. velocity of gas

C. pressure intensity of gas

D. discharge

12. 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__________________?
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A. 0.25

B. 1.0

C. none of the above

D. 0.5

13. Flow at constant rate through a tapering pipe is________________?
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A. non-uniform flow</strong>

B. correct answer is?

C. unsteady flow

D. uniform flow

E. steady flow
14. Coefficient of contraction for an external cylindrical mouthpiece is_________________?
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A. 0.7H

B. 1.00

C. 0.611

D. 0.855

15. Surge wave in a rectangular channel is an example of_________________?
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A. unsteady flow

B. uniform flow

C. correct answer is?

D. steady flow

E. non-uniform flow</strong>

16. Equation of continuity is based on the principle of conservation of_________________?
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A. none of the above

B. mass

C. momentum

D. energy

17. Which of the following statements is correct ?
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A. Lower critical Reynolds number is of no practical significance in pipe flow problems.

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

C. Lower critical Reynolds number has the value 2000 in pipe flow

D. Upper critical Reynolds number is significant in pipe flow problems.

18. The Prartdtl mixing length is_________________?
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A. maximum at the pipe wall

B. none of the above

C. zero at the pipe wall

D. independent of shear stress

19. Stanton diagram is a______________?
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A. semi-log plot of friction factor against Reynolds number

B. semi-log plot of friction factor against relative roughness

C. log-log plot of relative roughness against Reynolds number

D. log-log plot of friction factor against Reynolds number
20. 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__________________?
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A. 0.20 cm

B. 0.10 cm

C. 0.40 cm

D. 0.05 cm

21. The distance y from pipe boundary, at which the point velocity is equal to average velocity for turbulent flow, is________________?
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A. 0.577 R

B. 0.223 R

C. 0.423 R

D. 0.707 R

22. The speed of a pressure wave through a pipe depends upon________________?
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A. the bulk modulus for the fluid

B. the viscosity of fluid

C. the length of pipe

D. the original head

23. In which of the following the friction drag is generally larger than pressure drag?
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A. a sphere

B. an airfoil

C. a circular disc or plate held normal to flow

D. a cylinder

24. The value of friction factor f for smooth pipes for Reynolds number 106 is approximately equal to________________?
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A. 0.1

B. 0.01

C. 0.0001

D. 0.001

25. In series-pipe problems_______________?
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A. the discharge is same through each pipe

B. a trial solution is not necessary

C. the head loss is same through each pipe

D. the discharge through each pipe is added to obtain total discharge

26. Pascal-second is the unit of______________?
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A. pressure

B. dynamic viscosity

C. kinematic viscosity

D. surface tension

27. An ideal fluid is_______________?
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A. frictionless and incompressible

B. one which obeys Newtons law of viscosity

C. very viscous

D. frictionless and compressible

28. If the weight of a body immersed in a fluid exceeds the buoyant force, then the body will________________?
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A. float

B. rise until its weight equals the buoyant force

C. none of the above

D. tend to move downward and it may finally sink
29. The viscosity of a gas_______________?
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A. increases with increase in temperature

B. is independent of pressure for very high pressure intensities

C. decreases with increase in temperature

D. is independent of temperature

30. The discharge over a broad crested weir is maximum when the depth of flow is_______________?
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A. 2 H/3

B. H/3

C. H/2

D. 2 H/5

31. When a liquid rotates at a constant angular velocity about a vertical axis as a rigid body, the pressure intensity varies________________?
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A. inversely as the square of the radial distance

B. as the square of the radial distance

C. inversely as the radial distance

D. linearly with radial distance

32. The unit of kinematic viscosity is_______________?
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A. dyne-sec/cm2

B. cm2/sec

C. gm/cm2-sec

D. gm/cm-sec2

33. 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________________?
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A. 15 kN

B. 5kN

C. lOkN

D. 20 kN

34. Coefficient of velocity of venturimeter_________________?
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A. none of the above

B. is equal to the coefficient of discharge of venturimeter

C. is independent of Reynolds number

D. decreases with higher Reynolds number

35. When an ideal fluid flows past a sphere________________?
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A. lowest pressure intensity occurs at rear stagnation point

B. total drag is zero

C. lowest pressure intensity occurs at front stagnation point

D. highest intensity of pressure occurs around the circumference at right angles to flow

36. The motion of air mass in a tornado is a________________?
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A. forced vortex at center and free vortex outside

B. free vortex at center and forced vortex outside

C. free vortex motion

D. forced vortex motion

37. The position of center of pressure on a plane surface immersed vertically in a static mass of fluid is______________?
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A. always above the centroid of the area

B. none of the above

C. always below the centroid of the area

D. at the centroid of the submerged area

38. The distance from pipe boundary, at which the turbulent shear stress is one-third die wall shear stress, is_______________?
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A. 2/3 R

B. 1/3 R

C. 1/2 R

D. 3/4R

39. With the same cross-sectional area and immersed in same turbulent flow, the largest total drag will be on__________________?
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A. a circular disc of plate held normal to flow

B. a cylinder

C. a streamlined body

D. a sphere

40. 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________________?
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A. 4.2m

B. 3.75 m

C. 4.5m

D. 4.0 m

41. 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________________?
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A. the bubble will move to the front

B. the bubble will move to the rear </strong>

C. the ball will move to the front

D. d out which of the above statements are correct ?

E. the ball will move to the rear

42. The eddy viscosity for turbulent flow is______________?
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A. dependent on the flow

B. a function of temperature only

C. independent of the flow

D. a physical property of the fluid.

43. 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_________________?
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A. 0.223 D

B. 0.707 D

C. 0.423 D

D. 0.577 D
44. In a forced vortex motion, the velocity of flow is________________?
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A. directly proportional to the square of its radial distance from the 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 its radial distance from axis of rotation
45. In steady flow of a fluid, the total accele ration of any fluid particle______________?
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A. is independent of coordinates

B. is never zero

C. can be zero

D. is always zero

46. 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________________?
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A. 10 kN/m2

B. 12 kN/m2

C. 4 kN/m2

D. 14 kN/m2
47. The pitot tube is used to measure________________?
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A. stagnation pressure

B. velocity at stagnation point

C. dynamic pressure

D. static pressure

48. The boundary layer thickness in turbulent flow varies as______________?
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A. x,/2

B. x7

C. x4/5

D. x3/5

49. 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___________________?
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A. from reservoir A to reservoirs B and C

B. from reservoir C to reservoirs A and B

C. from reservoir B to reservoirs C and A

D. unpredictable

50. 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_______________?
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A. g

B. g/3

C. g/2

D. 2g/3