Fluid Mechanics MCQ Solved Paper for NDA

1. The Bernoulli's equation is based on the assumption that
A. There is no loss of energy of the liquid flowing
B. The velocity of flow is uniform across any cross-section of the pipe
C. No force except gravity acts on the fluid
D. All of the above
Answer : D

2. Free surface of a liquid tends to contract to the smallest possible area due to force of
A. Surface tension
B. Viscosity
C. Friction
D. Cohesion
Answer : A

3. General energy equation holds for
A. Steady flow
B. Turbulent flow
C. Laminar flow
D. Non-uniform flow
Answer : D

4. The specific gravity of water is taken as
A. 0.001
B. 0.01
C. 0.1
D. 1
Answer : D

5. The ratio of the inertia force to the elastic force is called
A. Reynold's number
B. Froude's number
C. Weber's number
D. Mach number
Answer : D

6. The highest efficiency is obtained with a channel of __________ section.
A. Circular
B. Square
C. Rectangular
D. Trapezoidal
Answer : D

7. In open channels, the specific energy is the
A. Total energy per unit discharge
B. Total energy measured with respect to the datum passing through the bottom of the channel
C. Total energy measured above the horizontal datum
D. Kinetic energy plotted above the free surface of water
Answer : B

8. The total pressure on a horizontally immersed surface is (where w = Specific weight of the liquid, A = Area of the immersed surface, and x = Depth of the centre of gravity of the immersed surface from the liquid surface)
A. wA
B. wx
C. wAx
D. wA/x
Answer : C

9. For measuring flow by a Venturimeter, if should be installed in
A. Vertical line
B. Horizontal line
C. Inclined line with flow downward
D. In any direction and in any location
Answer : D

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

11. An open tank containing liquid is moving with an acceleration on an inclined plane. The inclination of the free surface of the liquid will be __________ to the acceleration of the tank.
A. Equal to
B. Directly proportional
C. Inversely proportional
D. None of these
Answer : B

12. Hydrometer is used to determine
A. Specific gravity of liquids
B. Specific gravity of solids
C. Specific gravity of gases
D. Relative humidity
Answer : A

13. The buoyancy depends upon the
A. Weight of the liquid displaced
B. Pressure with which the liquid is displaced
C. Viscosity of the liquid
D. Compressibility of the liquid
Answer : A

14. When a body is placed over a liquid, it will float if
A. Gravitational force is equal to the up-thrust of the liquid
B. Gravitational force is less than the up-thrust of the liquid
C. Gravitational force is more than the up-thrust of the liquid
D. None of the above
Answer : B

15. A weir is said to be narrow-crested weir, if the width of the crest of the weir is __________ half the height of water above the weir crest.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : B

16. A channel is said to be of most economical cross-section, if
A. It gives maximum discharge for a given cross-sectional area and bed slope
B. It has minimum wetted perimeter
C. It involves lesser excavation for the designed amount of discharge
D. All of the above
Answer : D

17. The total pressure on the top of a closed cylindrical vessel of radius (r) completely filled up with liquid of specific weight (w) and rotating at (?) rad/s about its vertical axis, is
A. ? w ?² r²/4g
B. ? w ?² r³/4g
C. ? w ?² r?/4g
D. ? w ?² r²/2g
Answer : C

18. Property of a fluid by which molecules of different kinds of fluids are attracted to each other is called
A. Adhesion
B. Cohesion
C. Viscosity
D. Compressibility
Answer : A

19. When the coefficient of discharge (Cd) is 0.623, then the general equation for discharge over a rectangular weir is
A. 1.84 (L - 0.1nH)H^3/2
B. 1.84 (L - nH)H²
C. 1.84 (L - 0.1nH)H^5/2
D. 1.84 (L - nH)H³
Answer : A

20. Select the correct statement
A. Local atmospheric pressure depends upon elevation of locality only
B. Standard atmospheric pressure is the mean local atmospheric pressure a* sea level
C. Local atmospheric pressure is always below standard atmospheric pressure
D. A barometer reads the difference between local and standard atmospheric pressure
Answer : B

21. Uniform flow occurs when
A. The flow is steady
B. The flow is streamline
C. Size and shape of the cross section in a particular length remain constant
D. Size and cross section change uniformly along length
Answer : C

22. The meatcentric height of a ship is 0.6 m and the radius of gyration is 4 m. The time of rolling of a ship is
A. 4.1 s
B. 5.2 s
C. 10.4 s
D. 14.1 s
Answer : C

23. A water tank contains 1.3 m deep water. The pressure exerted by the water per metre length of the tank is
A. 2.89 kN
B. 8.29 kN
C. 9.28 kN
D. 28.9 kN
Answer : B

24. The flow in a pipe is neither laminar nor turbulent when Reynold number is
A. Less than 2000
B. Between 2000 and 2800
C. More than 2800
D. None of these
Answer : B

25. At the center line of a pipe flowing under pressure where the velocity gradient is zero, the shear stress will be
A. Minimum
B. Maximum
C. Zero
D. Could be any value
Answer : D

26. 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

27. A uniform body 3 m long, 2 m wide and 1 m deep floats in water. If the depth of immersion is 0.6 m, then the weight of the body is
A. 3.53 kN
B. 33.3 kN
C. 35.3 kN
D. None of these
Answer : C

28. A fluid having no viscosity is known as
A. Real fluid
B. Ideal fluid
C. Newtonian fluid
D. Non-Newtonian fluid
Answer : B

29. The vapour pressure over the concave surface is
A. Less man the vapour pressure over the plane surface
B. Equal to the vapour pressure over the plane surface
C. Greater than the vapour pressure over the plane surface
D. Zero
Answer : A

30. Hot wire anemometer is used to measure
A. Pressure in gases
B. Liquid discharge
C. Pressure in liquids
D. Gas velocities
Answer : D

31. Bulk modulus of a fluid __________ as the pressure increases.
A. Remain same
B. Decreases
C. Increases
D. None of these
Answer : C

32. The length AB of a pipe ABC in which the liquid is flowing has diameter (d1) and is suddenly enlarged to diameter (d2) at B which is constant for the length BC. The loss of head due to sudden enlargement is
A. (v? - v?)²/g
B. (v?² - v?²)/g
C. (v? - v?)²/2g
D. (v?² - v?²)/2g
Answer : C

33. The total energy line lies over the hydraulic gradient line by an amount equal to the
A. Pressure head
B. Velocity head
C. Pressure head + velocity head
D. Pressure head - velocity head
Answer : B

34. Choose the wrong statement
A. Any weight, floating or immersed in a liquid, is acted upon by a buoyant force
B. Buoyant force is equal to the weight of the liquid displaced
C. The point through which buoyant force acts, is called the center of buoyancy
D. Center of buoyancy is located above the center of gravity of the displaced liquid
Answer : D

35. The divergent portion of a Venturimeter is made longer than convergent portion in order to
A. Avoid the tendency of breaking away the stream of liquid
B. To minimise frictional losses
C. Both (A) and (B)
D. None of these
Answer : C

36. A flow is called hyper-sonic, if the Mach number is
A. Less than unity
B. Unity
C. Between 1 and 6
D. None of these
Answer : D

37. 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

38. 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 : B

39. The intensity of pressure at any point, in a liquid, is
A. Directly proportional to the area of the vessel containing liquid
B. Directly proportional to the depth of liquid from the surface
C. Directly proportional to the length of the vessel containing liquid
D. Inversely proportional to the depth of liquid from the surface
Answer : B

40. 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

41. Center of buoyancy is the
A. Centroid of the displaced volume of fluid
B. Center of pressure of displaced volume
C. Does not exist
D. None of the above
Answer : A

42. A vertical wall is subjected to a pressure due to one kind of liquid, on one of its sides. The total pressure on the wall per unit length is (where w = Specific weight of liquid, and H = Height of liquid)
A. wH
B. wH/2
C. wH²/2
D. wH²/3
Answer : C

43. 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

44. The specific weight of water in S.I. units is taken as
A. 9.81 kN/m³
B. 9.81 × 10³ N/m³
C. 9.81 × 10^-6 N/mm³
D. Any one of these
Answer : D

45. The loss of head at entrance in a pipe is (where v = Velocity of liquid in the pipe)
A. v²/2g
B. 0.5v²/2g
C. 0.375v²/2g
D. 0.75v²/2g
Answer : B

46. Newton's law of viscosity is a relationship between
A. Pressure, velocity and temperature
B. Shear stress and rate of shear strain
C. Shear stress and velocity
D. Rate of shear strain and temperature
Answer : B

47. Buoyant force is
A. The resultant force acting on a floating body
B. The resultant force on a body due to the fluid surrounding it
C. Equal to the volume of liquid displaced
D. The force necessary to maintain equilibrium of a submerged body
Answer : B

48. 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

49. The total pressure force on a plane area is equal to the area multiplied by the intensity of pressure at the Centroid, if
A. The area is horizontal
B. The area is vertical
C. The area is inclined
D. All of the above
Answer : D

50. Metacentric height is the distance between the metacentre and
A. Water surface
B. Center of pressure
C. Center of gravity
D. Center of buoyancy
Answer : C