Fluid Mechanics MCQ Solved Paper for UPSC CDS

1. A tank of uniform cross-sectional area (A) containing liquid upto height (H1) has an orifice of cross-sectional area (a) at its bottom. The time required to empty the tank completely will be
A. (2A?H?)/(C_d × a?2g)
B. (2AH?)/(C_d × a?2g)
C. (2AH?^3/2)/(C_d × a?2g)
D. (2AH?²)/(C_d × a?2g)
Answer : A

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

3. For pipes, laminar flow occurs when Reynolds number is
A. Less than 2000
B. Between 2000 and 4000
C. More than 4000
D. Less than 4000
Answer : A

4. A vessel of 4 m³ contains oil which weighs 30 kN. The specific weight of the oil is
A. 4.5 kN/m³
B. 6 kN/m³
C. 7.5 kN/m³
D. 10 kN/m³
Answer : C

5. The stability of a dam is checked for
A. Tension at the base
B. Overturning of the wall or dam
C. Sliding of the wall or dam
D. All of these
Answer : D

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

7. The discharge through a small rectangular orifice is given by (where Cd = Coefficient of discharge for the orifice, a = Cross-sectional area of the orifice, h = Height of the liquid above the centre of the orifice)
A. Q = Cd × a × 2gh
B. Q = (2/3). Cd × a × h
C. Q = (Cd × a)/?(2gh)
D. Q = (3Cd × a)/?(2h)
Answer : A

8. The body will float if the force of buoyancy is __________ the weight of the liquid displaced.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : C

9. The force exerted by a moving fluid on an immersed body is directly proportional to the rate of change of momentum due to the presence of the body. This statement is called
A. Newton's law of motion
B. Newton's law of cooling
C. Newton's law of viscosity
D. Newton's law of resistance
Answer : D

10. The length AB of a pipe ABC in which the liquid is flowing has diameter (d₁) and is suddenly contracted to diameter (d₂) at B which is constant for the length BC. The loss of head due to sudden contraction, assuming coefficient of contraction as 0.62, is
A. v?²/2g
B. v?²/2g
C. 0.5 v?²/2g
D. 0.375 v?²/2g
Answer : D

11. A piece weighing 3 kg in air was found to weigh 2.5 kg when submerged in water. Its specific gravity is
A. 1
B. 5
C. 7
D. 6
Answer : D

12. An odd shaped body weighing 7.5 kg and occupying 0.01 m3 volume will be completely submerged in a fluid having specific gravity of
A. 1
B. 1.2
C. 0.8
D. 0.75
Answer : D

13. Specific weight of water in S.I. units is equal to
A. 1000 N/m³
B. 10000 N/m³
C. 9.81 × 10³ N/m³
D. 9.81 × 10? N/m³
Answer : C

14. The center of pressure of a surface subjected to fluid pressure is the point
A. On the surface at which resultant pressure acts
B. On the surface at which gravitational force acts
C. At which all hydraulic forces meet
D. Similar to metacentre
Answer : A

15. 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

16. A fluid in equilibrium can't sustain
A. Tensile stress
B. Compressive stress
C. Shear stress
D. Bending stress
Answer : C

17. A fluid which obeys the Newton's law of viscosity is termed as
A. Real fluid
B. Ideal fluid
C. Newtonian fluid
D. Non-Newtonian fluid
Answer : C

18. A nozzle placed at the end of a water pipe line discharges water at a
A. Low pressure
B. High pressure
C. Low velocity
D. High velocity
Answer : D

19. The power absorbed (in watts) in overcoming the viscous resistance of a footstep bearing is
A. ? ?³ N² R² /1800 t
B. ? ?³ N² R? /1800 t
C. ? ?³ N² R² /3600 t
D. ? ?³ N² R? /3600 t
Answer : B

20. The units of dynamic or absolute viscosity are
A. Metres² per sec
B. kg sec/meter
C. Newton-sec per meter
D. Newton-sec² per meter
Answer : C

21. 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

22. 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

23. The power transmitted through the pipe is maximum when the head lost due to friction is equal to
A. One-fourth of the total supply head
B. One-third of the total supply head
C. One-half of the total supply head
D. Two-third of the total supply head
Answer : B

24. A manometer is used to measure
A. Low pressure
B. Moderate pressure
C. High pressure
D. Atmospheric pressure
Answer : C

25. The loss of head at exit of 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 : A

26. When a tube of smaller diameter is dipped in water, the water rises in the tube with an upward __________ surface.
A. Concave
B. Convex
C. Plane
D. None of these
Answer : A

27. 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

28. The region between the separation streamline and the boundary surface of the solid body is known as
A. Wake
B. Drag
C. Lift
D. Boundary layer
Answer : A

29. A flow through an expanding tube at constant rate is called
A. Steady uniform flow
B. Steady non-uniform flow
C. Unsteady uniform flow
D. Unsteady non-uniform flow
Answer : B

30. The specific weight of sea water is __________ that of pure water.
A. Same as
B. Less than
C. More than
D. None of these
Answer : C

31. The discharge through a channel of circular section will be maximum when the depth of water is __________ the diameter of the circular channel.
A. 0.34 times
B. 0.67 times
C. 0.81 times
D. 0.95 times
Answer : D

32. The most economical section of a rectangular channel is one which has hydraulic mean depth or hydraulic radius equal to
A. Half the depth
B. Half the breadth
C. Twice the depth
D. Twice the breadth
Answer : A

33. 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

34. Which of the following meters is not associated with viscosity?
A. Red wood
B. Say bolt
C. Engler
D. Orsat
Answer : D

35. The flow of water through the hole in the bottom of a wash basin is an example of
A. Steady flow
B. Uniform flow
C. Free vortex
D. Forced vortex
Answer : C

36. Center of pressure on an inclined plane is
A. At the Centroid
B. Above the Centroid
C. Below the Centroid
D. At metacentre
Answer : C

37. Density of water is maximum at
A. 0° C
B. 0° K
C. 4° C
D. 100° C
Answer : C

38. The bulk modulus of elasticity
A. Has the dimensions of 1/pressure
B. Increases with pressure
C. Is large when fluid is more compressible
D. Is independent of pressure and viscosity
Answer : B

39. 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

40. When a cylindrical vessel containing liquid is resolved, the surface of the liquid takes the shape of
A. A triangle
B. A paraboloid
C. An ellipse
D. None of these
Answer : B

41. Choose the wrong statement. Alcohol is used in manometer, because
A. Its vapour pressure is low
B. It provides suitable meniscus for the inclined tube
C. Its density is less
D. It provides longer length for a given pressure difference
Answer : A

42. 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

43. 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

44. Froude's number is the ratio of inertia force to
A. Pressure force
B. Elastic force
C. Gravity force
D. Surface tension force
Answer : C

45. The flow in which each liquid particle has a definite path and their paths do not cross each other is called
A. One dimensional flow
B. Streamline flow
C. Steady flow
D. Turbulent flow
Answer : B

46. The total pressure on the surface of a vertical sluice gate 2 m x 1 m with its top 2 m surface being 0.5 m below the water level will be
A. 500 kg
B. 1000 kg
C. 1500 kg
D. 2000 kg
Answer : D

47. 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

48. Surface tension has the units of
A. Newton-sec/m
B. Newton-m/sec
C. Newton/m
D. Newton
Answer : C

49. Liquids
A. Cannot be compressed
B. Occupy definite volume
C. Are not affected by change in pressure and temperature
D. None of the above
Answer : D

50. Flow of water in a pipe about 3 metres in diameter can be measured by
A. Orifice plate
B. Venturimeter
C. Rotameter
D. Pitot tube
Answer : D