1000+ Fluid Mechanics MCQ for GATE [Solved]

1. The force present in a moving liquid is
A. Inertia force
B. Viscous force
C. Gravity force
D. All of these
Answer : D

2. The discharge over a rectangular notch is
A. Inversely proportional to H^3/2
B. Directly proportional to H^3/2
C. Inversely proportional to H^5/2
D. Directly proportional to H^5/2
Answer : B

3. Stoke is the unit of
A. Kinematic viscosity in C. G. S. units
B. Kinematic viscosity in M. K. S. units
C. Dynamic viscosity in M. K. S. units
D. Dynamic viscosity in S. I. units
Answer : A

4. A piece of metal of specific gravity 7 floats in mercury of specific gravity 13.6. What fraction of its volume is under mercury?
A. 0.5
B. 0.4
C. 0.515
D. 0.5
Answer : C

5. Falling drops of water become spheres due to the property of
A. Adhesion
B. Cohesion
C. Surface tension
D. Viscosity
Answer : C

6. The discharge of a depressed nappe is 6 to 7 percent __________ that of a free nappe.
A. Less than
B. More than
C. Equal to
D. None of these
Answer : B

7. 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

8. A square surface 3 m × 3 m lies in a vertical line in water pipe its upper edge at water surface. The hydrostatic force on square surface is
A. 9,000 kg
B. 13,500 kg
C. 18,000 kg
D. 27,000 kg
Answer : B

9. Water is __________ liquid.
A. A compressible
B. An incompressible
C. Both A and B
D. None of these
Answer : B

10. 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

11. The diameter of the nozzle (d) for maximum transmission of power is given by (where D = Diameter of pipe, f = Darcys coefficient of friction for pipe, and l = Length of pipe)
A. d = (D?/8fl)^1/2
B. d = (D?/8fl)^1/3
C. d = (D?/8fl)^1/4
D. d = (D?/8fl)^1/5
Answer : C

12. A balloon lifting in air follows the following principle
A. Law of gravitation
B. Archimedes principle
C. Principle of buoyancy
D. All of the above
Answer : D

13. Barometer is used to measure
A. Pressure in pipes, channels etc.
B. Atmospheric pressure
C. Very low pressure
D. Difference of pressure between two points
Answer : B

14. 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

15. A flow in which the quantity of liquid flowing per second is constant, is called __________ flow.
A. Steady
B. Streamline
C. Turbulent
D. Unsteady
Answer : A

16. Resultant pressure of the liquid in the case of an immersed body acts through
A. Centre of gravity
B. Centre of pressure
C. Metacentre
D. Centre of buoyancy
Answer : B

17. A hemispherical tank of radius (R) has an orifice of cross-sectional area (a) at its bottom and is full of liquid. The time required to empty the tank completely is
A. 14? R^1/2/15C_d × a ?(2g)
B. 14? R^3/2/15C_d × a ?(2g)
C. 14? R^5/2/15C_d × a ?(2g)
D. 14? R^7/2/15C_d × a ?(2g)
Answer : C

18. The flow in which the velocity vector is identical in magnitude and direction at every point, for any given instant, is known as
A. One dimensional flow
B. Uniform flow
C. Steady flow
D. Turbulent flow
Answer : B

19. When a tank containing liquid moves with an acceleration in the horizontal direction, then the free surface of the liquid
A. Remains horizontal
B. Becomes curved
C. Falls on the front end
D. Falls on the back end
Answer : C

20. 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

21. The top of the weir over which the water flows is known as
A. Sill or crest
B. Nappe or vein
C. Orifice
D. None of these
Answer : A

22. 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

23. 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

24. A bucket of water is hanging from a spring balance. An iron piece is suspended into water without touching sides of bucket from another support. The spring balance reading will
A. Increase
B. Decrease
C. Remain same
D. Increase/decrease depending on depth of immersion
Answer : C

25. 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

26. An average value of coefficient of velocity is
A. 0.62
B. 0.76
C. 0.84
D. 0.97
Answer : D

27. An error of 1% in measuring head over the apex of the notch (H) will produce an error of _________ in discharge over a triangular notch.
A. 1 %
B. 1.5 %
C. 2 %
D. 2.5 %
Answer : D

28. The flow in a pipe or channel is said to be non-uniform when
A. The liquid particles at all sections have the same velocities
B. The liquid particles at different sections have different velocities
C. The quantity of liquid flowing per second is constant
D. Each liquid particle has a definite path
Answer : B

29. A hydraulic press has a ram of 15 cm diameter and plunger of 1.5 cm. It is required to lift a weight of 1 tonne. The force required on plunger is equal to
A. 10 kg
B. 100 kg
C. 1000 kg
D. 1 kg
Answer : A

30. 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

31. Dynamic viscosity of most of the liquids with rise in temperature
A. Increases
B. Decreases
C. Remain unaffected
D. Unpredictable
Answer : B

32. Euler's number is the ratio of __________ force to pressure force.
A. Inertia
B. Gravity
C. Viscous
D. None of these
Answer : A

33. A flow in which the viscosity of fluid is dominating over the inertia force is called
A. Steady flow
B. Unsteady flow
C. Laminar flow
D. Turbulent flow
Answer : C

34. The factional resistance of a pipe varies approximately with __________ of the liquid.
A. Pressure
B. Velocity
C. Square of velocity
D. Cube of velocity
Answer : C

35. In a free vortex motion, the radial component of velocity everywhere is
A. Maximum
B. Minimum
C. Zero
D. Nonzero and finite
Answer : C

36. 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

37. The most economical section of a trapezoidal channel is one which has hydraulic mean depth equal to
A. 1/2 × depth
B. 1/2 × breadth
C. 1/2 × sloping side
D. 1/4 × (depth + breadth)
Answer : A

38. In order to measure the flow with a Venturimeter, it is installed in
A. Horizontal line
B. Inclined line with flow upwards
C. Inclined line with flow downwards
D. Any direction and in any location
Answer : D

39. 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

40. 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

41. A model of torpedo is tested in a towing tank at a velocity of 25 m/sec. The prototype is expected to attain a velocity of 5 m/sec. What model scale has been used?
A. 1 : 5
B. 1 : 2.5
C. 1 : 25
D. 1 : ?5
Answer : A

42. The dynamic viscosity of gases __________ with rise in temperature.
A. Remain unaffected
B. Increases
C. Decreases
D. None of these
Answer : B

43. 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

44. 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

45. 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 bring the liquid level from H1 to H2 will be
A. 2A × ?H?/C_d × a × ?(2g)
B. 2A × ?H?/C_d × a × ?(2g)
C. 2A × (?H? - ?H?)/C_d × a × ?(2g)
D. 2A × (?H^3/2 - ?H3/2)/C_d × a × ?(2g)
Answer : C

46. An object having 10 kg mass weighs 9.81 kg on a spring balance. The value of 'g' at this place is
A. 10 m/sec²
B. 9.81 m/sec²
C. 9.75 m/sec²
D. 9 m/sec
Answer : A

47. Re-entrant or Borda's mouthpiece is an __________ mouthpiece.
A. Internal
B. External
C. Both A and B
D. None of these
Answer : A

48. Which of the following manometer has highest sensitivity?
A. U-tube with water
B. Inclined U-tube
C. U-tube with mercury
D. Micro-manometer with water
Answer : D

49. Euler's equation in the differential form for the motion of liquids is given by
A. dp/? + g.dz + v.dv = 0
B. dp/? - g.dz + v.dv = 0
C. ?.dp + g.dz + v.dv = 0
D. ?.dp - g.dz + v.dv = 0
Answer : A

50. An internal mouthpiece is said to be running __________ if the length of the mouthpiece is more than three times the diameter of the orifice.
A. Free
B. Partially
C. Full
D. None of these
Answer : C