DRDO - Fluid Mechanics 1000+ MCQ [Solved] PDF Download

1. The hydraulic mean depth for a circular pipe of diameter (d) is
A. d/6
B. d/4
C. d/2
D. d
Answer : B

2. Dimensions of surface tension are
A. ML°T?²
B. ML°T
C. ML r²
D. ML²T²
Answer : A

3. Venturimeter is used to
A. Measure the velocity of a flowing liquid
B. Measure the pressure of a flowing liquid
C. Measure the discharge of liquid flowing in a pipe
D. Measure the pressure difference of liquid flowing between two points in a pipe line
Answer : C

4. The value of bulk modulus of a fluid is required to determine
A. Reynold's number
B. Froude's number
C. Mach number
D. Euler's number
Answer : C

5. The centre of gravity of the volume of the liquid displaced by an immersed body is called
A. Centre of gravity
B. Centre of pressure
C. Metacentre
D. Centre of buoyancy
Answer : D

6. According to Bazin's formula, the discharge over a rectangular weir is mL2g x H^3/2where m is equal to
A. 0.405 + (0.003/H)
B. 0.003 + (0.405/H)
C. 0.405 + (H/0.003)
D. 0.003 + (H/0.405)
Answer : A

7. The loss of pressure head in case of laminar flow is proportional to
A. Velocity
B. (Velocity)²
C. (Velocity)³
D. (Velocity)⁴
Answer : A

8. The pressure in the air space above an oil (sp. gr. 0.8) surface in a tank is 0.1 kg/cm. The pressure at 2.5 m below the oil surface will be
A. 2 metres of water column
B. 3 metres of water column
C. 3.5 metres of water column
D. 4 m of water column
Answer : B

9. The shear stress-strain graph for a Newtonian fluid is a
A. Straight line
B. Parabolic curve
C. Hyperbolic curve
D. Elliptical
Answer : A

10. Choose the wrong statement
A. Viscosity of a fluid is that property which determines the amount of its resistance to a shearing force
B. Viscosity is due primarily to interaction between fluid molecules
C. Viscosity of liquids decreases with increase in temperature
D. Viscosity of liquids is appreciably affected by change in pressure
Answer : D

11. The theoretical velocity of jet at vena contracta is (where H = Head of water at vena contracta)
A. 2gH
B. H × ?(2g)
C. 2g × ?H
D. ?(2gh)
Answer : D

12. When the pressure intensity at a point is more than the local atmospheric pressure, then the difference of these two pressures is called
A. Gauge pressure
B. Absolute pressure
C. Positive gauge pressure
D. Vacuum pressure
Answer : C

13. A structure used to dam up a stream or river over which the water flows is called
A. Orifice
B. Notch
C. Weir
D. Dam
Answer : C

14. Coefficient of resistance is the ratio of
A. Actual velocity of jet at vena-contracta to the theoretical velocity
B. Area of jet at vena-contracta to the area of orifice
C. Loss of head in the orifice to the head of water available at the exit of the orifice
D. Actual discharge through an orifice to the theoretical discharge
Answer : C

15. The discharge through a channel of trapezoidal section is maximum when
A. Width of channel at the top is equal to twice the width at the bottom
B. Depth of channel is equal to the width at the bottom
C. The sloping side is equal to half the width at the top
D. The sloping side is equal to the width at the bottom
Answer : C

16. The discharge in an open channel corresponding to critical depth is
A. Zero
B. Minimum
C. Maximum
D. None of these
Answer : C

17. The pressure in Pascals at a depth of 1 m below the free surface of a body of water will be equal to
A. 1 Pa
B. 91 Pa
C. 981 Pa
D. 9810 Pa
Answer : D

18. Property of a fluid by which its own molecules are attracted is called
A. Adhesion
B. Cohesion
C. Viscosity
D. Compressibility
Answer : B

19. The viscosity of water is __________ than that of mercury.
A. Higher
B. Lower
C. Same as
D. None of these
Answer : A

20. The siphon will work satisfactorily, if the minimum pressure in the pipe is __________ vapour pressure of liquid.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : C

21. The power transmitted through a pipe is (where w = Specific weight in N/m³, and Q = Discharge in m³/s)
A. w × Q × H
B. w × Q × hf
C. w × Q (H - hf)
D. w × Q (H + hf)
Answer : C

22. The sheet of water flowig over a notch or a weir is known as
A. Sill or crest
B. Nappe or vein
C. Orifice
D. None of these
Answer : B

23. Kinematic viscosity is dependent upon
A. Pressure
B. Distance
C. Density
D. Flow
Answer : C

24. Reynold's number is the ratio of inertia force to
A. Pressure force
B. Elastic force
C. Gravity force
D. Viscous force
Answer : D

25. The fluid forces considered in the Navier Stokes equation are
A. Gravity, pressure and viscous
B. Gravity, pressure and turbulent
C. Pressure, viscous and turbulent
D. Gravity, viscous and turbulent
Answer : A

26. The conditions for the stable equilibrium of a floating body are
A. The metacentre should lie above the center of gravity
B. The center of buoyancy and the center of gravity must lie on the same vertical line
C. A righting couple should be formed
D. All the above are correct
Answer : D

27. If cohesion between molecules of a fluid is greater than adhesion between fluid and glass, then the free level of fluid in a dipped glass tube will be
A. Higher than the surface of liquid
B. The same as the surface of liquid
C. Lower than the surface of liquid
D. Unpredictable
Answer : C

28. The maximum discharge over a broad crested weir is
A. 0.384 C_d × L × H^1/2
B. 0.384 C_d × L × H^3/2
C. 1.71 C_d × L × H^1/2
D. 1.71 C_d × L × H^3/2
Answer : D

29. In a depressed nappe
A. The pressure below the nappe is atmospheric
B. The pressure below the nappe is negative
C. The pressure above the nappe is atmospheric
D. The pressure above the nappe is negative
Answer : B

30. The pressure intensity in kN/m2 (or kPa) at any point in a liquid is (where w = Specific weight of liquid, and h = Depth of liquid from the surface)
A. w
B. wh
C. w/h
D. h/w
Answer : B

31. The unit of kinematic viscosity in S. I. units is
A. N-m/s
B. N-s/m²
C. m²/s
D. N-m
Answer : C

32. When the Mach number is more than 6, the flow is called
A. Sub-sonic flow
B. Sonic flow
C. Super-sonic flow
D. Hyper-sonic flow
Answer : D

33. Capillary action is due to the
A. Surface tension
B. Cohesion of the liquid
C. Adhesion of the liquid molecules and the molecules on the surface of a solid
D. All of the above
Answer : D

34. The hydraulic gradient line lies over the centre line of the pipe by an amount equal to the
A. Pressure head
B. Velocity head
C. Pressure head + velocity head
D. Pressure head - velocity head
Answer : A

35. Which of the following instrument can be used for measuring speed of a submarine moving in deep sea?
A. Venturimeter
B. Orifice plate
C. Hot wire anemometer
D. Pitot tube
Answer : D

36. Viscous force is the __________ of shear stress due to viscosity and cross-section area of flow.
A. Sum
B. Different
C. Product
D. Ratio
Answer : C

37. Euler's dimensionless number relates the following
A. Inertial force and gravity
B. Viscous force and inertial force
C. Viscous force and buoyancy force
D. Pressure force and inertial force
Answer : D

38. The units of kinematic viscosity are
A. Metres² per sec
B. kg sec/metre
C. Newton-sec per metre
D. Newton-sec per metre
Answer : A

39. The specific weight of water is 1000 kg/m3
A. At normal pressure of 760 mm
B. At 4°C temperature
C. At mean sea level
D. All the above
Answer : D

40. The purpose of a surge tank is
A. To control the pressure variations due to rapid changes in the pipe line flow
B. To eliminate water hammer possibilities
C. To regulate flow of water to turbines by providing necessary retarding head of water
D. All of the above
Answer : D

41. The pressure of air __________ with the increase of height from the surface of the earth.
A. Does not change
B. Decreases
C. Increases
D. None of these
Answer : B

42. In a broad-crested weir, the discharge is maximum if the head of water on the downstream side of weir is __________ the head of water on the upstream side of weir.
A. Equal to
B. One-third
C. Two-third
D. Three-fourth
Answer : C

43. The discharge over a right angled notch is (where H = Height of liquid above the apex of notch)
A. (8/15) C_d. 2g. H
B. (8/15) C_d. 2g. H^3/2
C. (8/15) C_d. 2g. H²
D. (8/15) C_d. 2g. H^5/2
Answer : D

44. Surface energy per unit area of a surface is numerically equal to
A. Atmospheric pressure
B. Surface tension
C. Force of adhesion
D. Force of cohesion
Answer : B

45. A venturi-flume is used to measure
A. Pressure of liquid
B. Discharge of liquid
C. Pressure difference between two points in a channel
D. Pressure difference between two points in a pipe
Answer : B

46. The process of diffusion of one liquid into the other through a semi permeable membrane is called
A. Viscosity
B. Osmosis
C. Surface tension
D. Cohesion
Answer : B

47. The intensity of pressure at any point, in a liquid, is __________ to the depth of liquid from the surface.
A. Equal
B. Directly proportional
C. Inversely proportional
D. None of these
Answer : B

48. With an increase in size of tube, the rise or depression of liquid in the tube due to surface tension will
A. Decrease
B. Increase
C. Remain unchanged
D. Depend upon the characteristics of liquid
Answer : A

49. The property by virtue of which a liquid opposes relative motion between its different layers is called
A. Surface tension
B. Coefficient of viscosity
C. Viscosity
D. Osmosis
Answer : C

50. The ratio of the inertia force to the viscous force is called
A. Reynold's number
B. Froude's number
C. Weber's number
D. Euler's number
Answer : A