300+ Basic Mechanical Engineering Questions and Answers PDF

BASIC MECHANICAL ENGINEERING Interview Questions :-

1. What parameters influence the tool life ?

1. Tool material
2. Work material
3. Speed, feed and depth of cut
4. Tool geometry work system
5. Cutting fluid
6. Built up edge
7. Vibration behaviour of the machine tool.

2. Mention the function of intermediate stage in a generalised measurement system.

• Amplify signal without affecting its waveform
• Remove unwanted noise signals that tend to obscure the input
• Capable of doing other conditioning like differentiation/integration, A/D conversion etc.

3. What is a signal flow graph ?
A signal flow graph of a system is a graphical model in which nodes represent the system variables and directed branches between the nodes represent relationship between the variables. In a signal flow graph, a forward path originates from the input mode and terminates at output mode without encountering any mode more than once.

4. Explain the difference between rotational and irrotational flow.
In rotational flow the vorticity is non zero and in irrotational flow it is zero. In irrota¬tional flow the net rotation of a fluid element about its own mass centre is zero as it moves from one place to another. For it, dv/dx = du/dy.

5. Define the term stability of a feed back control system ?
A system is said to be stable if the output of a system after fluctuations, variations or oscilla-tions, settles at a reasonable value for any change in input.

6. What is meant by precision ?
Precision is defined as the ability of instrument to reproduce a certain set of readings within a given accuracy.

7. What is boundary layer ?
Boundary layer is the fluid layer in the neighbourhood of a solid boundary where the effects of fluid friction are predominant.

8. On what account the boundry layer exists ?
Boundary layer m fluid flow exists on account of fluid density.

9. Explain the difference between laminar flow and turbulent flow.
In laminar flow the fluid particles move along smooth, regular paths which can be pre¬dicted in well advance. Turbulent flow is characterised by random and erratic movements of fluid particles resulting in formation of eddies. For flow to be laminar in a pipe, the Reynold’s number is less than 2000 and for flow to be turbulent it is greater than 4000.

10. What is the difference between path line and stream line ?
A path line is a curve traced by a single fluid particle during its motion. A stream line is an imaginary line drawn in a flow field such that a tangent drawn at any point on this line represents the direction of the velocity vector. There is no flow across the stream line.

11. What is the difference between steady and unsteady flow ?
In steady flow the velocity at a given point does not change with time whereas in unsteady flow it changes with time.

12. What is stagnation point and stagnation pressure ?
A stagnation point is one at which velocity is zero. Stagnation pressure is the sum of static pressure and dynamic pressure.

13. What is the hydraulic-grade line ?
It is the line which shows tne variation of piezometric head.

14. Under what condition the thickness of thermal boundary layer and hydrody-namic boundary layer is same ? When Prandtl number is equal to unity.

15. What keeps the shaft in floating condition in hydrodynamic journal bearing ?
Hydrodynamic pressure developed in the lubricant.

16. Why the elements of higher pairs must be force closed ?
This is necessary to provide completely constrained motion.

17. What is the value of coefficient of friction for ball bearing ?
Ans: 0.1 to 0.25.

18. Why belts are subject to creep ?
Due to uneven extension and contraction of belt.

19. What is the ratio of damping coefficient to critical damping coefficient called ?
Damping factor.

20. In which type of lubrication the starting friction is low ?
In hydrostatic lubrication.

21. Whether Bernoulli’s equation is applicable for streamline straight and rotational flows ?
Ans: Yes.

22. When a plate slides over a parallel plate, what is the relationship between vis¬cous force and the lubricant thickness ?

They are directly proportional.

23. How the stability of empty ship increased.
By adding ballasts at the bottom level.

24. Define Froude number.
It is the square root of ratio of inertia force to gravity force.

25. What for Maning’s formula used ?
It is used to determine velocity of flow in pipe.

26. What is the maximum efficiency of power transmission through a pipe ?
66.67%.

27. What is the necessary and sufficient condition for bodies in floatation to be in stable equilibrium ?
Centre of gravity of body should be located below metacentre.

28. Under what condition the thermal boundary layer thickness will be equal to the hydrodynamic boundary layer thickness ?

When Prandtl number is unity.

29. How laminar boundary layer thickness varies on a flat plate ?
It is proportional to the square root of the distance from the leading edge.

30. Name the axial flow reaction turbine with adjustable vanes.
Kaplan turbine.

31. Define the degree of reaction of a turbomachine.
It is the ratio of total pressure change in the rotor to that in the stage.

32. What is meant by relative stability ?
If the system is found to be stable, then it is necessary to know the stable strength or degree of stability which is called relative stability. Phase margin and gain margins are the measures of relative stability.

33. On what factors the efficiency of a centrifugal pump depends ?
The efficiency of a centrifugal pump depends on size, speed and type number.

34. Define transducer ?
Transducer is an element which converts the signal from one physical form to another without changing the information content of the signal.

35. A 200 mm impeller of centrifugal pump develops discharge head of 2 kg/cm2. If discharge head is required as 8 kg/cm2, what should be diameter of impeller. Ans: 400 mm.

36. Why thin-plate orifice is frequently recommended for flow measurement in most of the cases ?
It is recommended because of its high accuracy, low cost, and extreme flexibility.

37. How the water flow from a hydrant in a city water system measured ?
It can be measured by allowing the flow of water from a hydrant and noting down the horizontal distance (x) where jet strikes the ground and the vertical distance (y) of outlet from ground.
Then flow = area of hydrant x

38. For the same size, length and condition of pipe, how the friction head loss changes if pipe size is varied.
Under same flow conditions the friction head loss increases as the size change to the 4.8th power.

39. How does the capacity changes in pipe flow with increase in pipe diameter if head is constant ?
At constant head, capacity is proportional to d25. .

40. How does the head change in pipe flow with change in diameter, if capacity is constant.
At constant capacity, head is proportional to

41. How head varies in pipe flow with change in flow, if pipe diameter is same.
At constant diameter, head is proportional to (flow)2.

42. Give some properties of errors ?

• Errors give the difference between the measured-value and the true value
• Accuracy of a measurement system is measured in terms of error
• A study of error helps in finding the reliability of the results.

43. Define the term contraction coefficient.
The ratio of area of jet (contracted) and the cross section of the orifice.

44. What for pycnometer is used ?
Pycnometer is used to measure specific gravity of the liquid.

45. How may types of bonded strain gauges used ?

• Fine wire strain gauge
• Metal foil strain gauge
• Piezo resistive gauge.

46. Name various functional elements of an instrumental system ?
(1) Primary sensing element
(2) Variable conversion (or) transducer element
(3) Variable manipulation element
(4) Data transmission element
(5) Data processing element
(6) Data presentation element
(7) Data storage and playback element.

47. Name the three stages of a generalised measuring system.
(i) Sensing and converting the input to a convenient and practicable form.
(ii) Processing/manipulating the measured variable.
(iii) Presenting the processed measured variable in quantitative form.

48. How is a Pelton turbine braked ?
A pelton wheel is braked by a nozzle directing a jet on the back of the buckets.

49. What is static pressure ? How is it measured.
The pressure caused on the walls of a pipe due to a fluid at rest inside the pipe or due to the flow of a fluid parallel to walls of the pipe is called static pressure. This static pressure is measured by inserting a pressure measuring tube into the pipe carrying the fluid so that the tube is at right angle to the fluid flow path.

50. What are the requirements of a control system ?
Stability, accuracy and speed of response are the three requirements of control system.

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51. What is the difference between weir, and submerged weir.
Any obstruction of a streamflow over which water flows is weir. When the downstream water level rises over the weir crest, it is called submerged weir.

52. What is the difference between spillway and siphon spillway ?
Spillway is an essential part of a large dam and provides an efficient and safe means of releasing flood water that exceeds the design capacity of the reservoir.
Siphon spillway is spillway designed to discharge water in a closed conduit under negative pressure.

53. What is the difference between culverts, stilling basin, and standpipe ?
Culverts are built at the points of lowest valley to pass water across the embankments of highways or railroads.
Stilling basin is transitional energy dissipating structure to avoid the damaging process by a highly accelerated spilled water.
Standpipe is used principally for alleviating the transient pressures in large pipeline system. It also works as a pressure relief valve for the upstream pipe during the turbine shut off.

54. What do you understand by run-of-river scheme in hydro power generation ?
A scheme in which the discharge is varying and only that much water can be utilised for conversion as available in the river.

55. What is the difference between firm power and secondary power in hydro power plants ?
The approximate constant and continuous power which is assured at power station and would be available throughout the year is called firm power.
In run-of-the river schemes which are generally designed for % availability of water, the firm power would be available for at least % of the years during the life of the scheme. However in some years discharge in the river may be more than % availability discharge and some extra power known as secondary power can be generated.

56. What is the criterion for determining economic diameter of power tunnel ?
The economic diameter of a power tunnel is determined such that the total value of following two factors is least
(i) annual loss of revenue on account of power head lost due to friction.
(ii) recurring annual expenditure.

57. What are the three functions served by a surge tank in a hydro plant ?
The three functions served by a surge tank are
(i) flow regulation – act as a reservoir for acceptance or delivery of water to meet requirements of load changes.
(ii) water-hammer relief or pressure regulation.
(iii) improvement in speed regulation.

58. What is the criterion to determine the economic diameter of penstock ?
The economic diameter of a penstock required to carry a discharge is the one at which annual costs due to the greater investment do not exceed the annual value of resulting increment energy output.

59. If jet ratio for a pelton wheel is 12 then number of buckets should be …. ?
0.5 x 12+ 15 = 21.

60. What is the difference between anti-friction and hydrostatic bearings ?
In anti-friction bearings rolling components are introduced between the sliding surfaces. In hydrostatic bearings lubricant is supplied at a high pressure to a pocket in the bearing.

61. What is inviscid fluid ?
It is the frictionless fluid.

62. State law of conservation of momentum ?
The ratio of change of momentum of a mass of fluid is equal to the vector sum of all external forces acting on it.

63. Define turbulent flow ?
Flow in which adjacent layers mix continuously, so that the flow pattern is unsteady, full of eddies, and apparently without any mathematically expressible regularity.

64. Define Reynold’s law of similitude ?
Two geometrically similar flow systems subject only to friction and inertia forces are dy¬namically similar if both have the same ‘Reynolds’ number.

65. What is the difference between boundary lubrication and fluid film lubrication ?
In boundary lubrication condition the ratio of thickness of lubrication film to surface roughness (CLA value) is less than 1 and for fluid film lubrication condition this ratio is greater than 5 and less than 100.

66. A bearing in which hydrodynamic pressure is generated due to rotation of jour¬nal is called… ?
Journal bearing.

67. For a journal running in a bearing clockwise at steady state, where will be the minimum clearance ?
To the left of the load line.

68. Out of impulse and reaction type hydraulic turbines, which has higher specific speed ?
Reaction turbine.

69. What is order of the system.
The order of the system is the order of the highest derivative of the ordinary differential equation with constant coefficients which defines the system mathematically.

70. What is Bode plot ?
Bode plot is a logarithmic plot used to represent transfer functions. The Bode plot consists of two plots namely.
(i) The plot of magnitude in db (on linear scale) vs. frequency to (on log scale)
(ii) The plot of phase angle in degrees (on linear scale) vs. frequency co (on log scale)

71. Navier stokes equation represents the conservation of which quantity ?
Momentum.

72. What are the characteristics of precision ?
(i) If a number of measurements are made on same true value, the degree of closeness of these measurements gives precision
(ii) It is a measure of the degree of repeatability or reproducibility of the measuring system.

73. What is meant by loading ?
During the act of measurement the measuring instrument takes energy from the signal source or measured medium and thus the signal source is altered. This effect is called loading.

74. Give two uses of Bode plots.
(i) They are the logarithmic plots used to represent transfer functions
(ii) They are used in the calculation of gain margin and phase margin.

75. What is the name of nondimensional group for ratio of inertia force to gravity force.
Froude number.

76. The head loss in a fully developed laminar flow in a circular pipe due to friction is directly proportional to … ?
Square of mean velocity.

77. For what type of flow, the streamlines, pathlines and streaklines are virtually identical ?
Steady flow.

78. How the streamlines and equipotential lines are related in a flow field ?
They are orthogoial everywhere in the flow field.

79. Under what kind and condition of a fluid the velocity potential exists ?
Irrotational flow.

80. Where should centre of gravity of a body lie for it to float in stable equilibrium ?
e.g. should be located below the metacentre.

81. For fully developed flow through a pipe, what is the ratio of maximum to average velocity ?
Ans: 2.

82. Out of centrifugal, axial and positive displacement pumps, which has maximum specific speed and which has minimum ?
Axial pump has maximum specific speed and reciprocating pump has minimum.

83. Specific speed of a turbine is 800. What type of turbine is this ?
Kaplan turbine.

84. In which type of lubrication system the starting friction is low ?
Hydrostatic lubrication.

85. At which point the cavitation is most likely to occur in a hydel plant ?
At turbine rotor exit.

86. What is the difference between lower pair and higher pair ?
In a kinematic pair, if the elements have surface contact when in motion, the pair is called lower pair and if elements have line or point contact the pair is called higher pair.

87. What do you understrand by inversions and how many inversions are possible in a kinematic chain having ‘n’ links ?
Inversions are different mechanisms obtained by fixing different links in a kinematic chain but keeping relative motions of links unchanged with respecat to one another. A kinematic chain with ‘n’ links can have ‘n’ inversions.

88. What is the difference between basic kinematic chain and compound kinematic chain ? What is the criteria for a chain to be constrained ?
A basic kinematic chain consists of four kinematic links and a compound kinematic chain is a constrained chain of more than four links. A chain is constrained if no. of binary joints and half of number of higher pairs is equal to 3/2 of no. of links minus 2.

89. What is the difference between a machine and a mechanism ?
A mechanism consists of links forming a constrained kinematic chain. Its function is ba¬sically to transmit or modify motion. A machine is a mechanism but here we are concerned with forces to be transmitted and it is used to modify mechanical work.

90. In which type of motion, acaceleration is directly proportional to displacement ?
SHM.

91. What is the function of a transducer element ?
The function of a transducer element is to sense and convert the desired input into a more convenient and practicable form to be handled by measurement system.

92. What is the direction of tangential acceleration ?
The direction of tangential acceleration may be same or opposite to that of angular velocity.

93. What is the number of degrees of freedom constrained in each case by the kinematic pairs.
(i) Itevolute pair, (ii) cylindrical pair, (iii) Screw pair, (iv) Spherical pair.
Ans: (i) Revolute pair—single degree of freedom.
(ii) cylindrical pair—two degrees of freedom.
(iii) Screw pair—one degree of freedom.
(iv) spherical pair—three degrees of freedom.

94. What is the purpose of D-slide valve in steam engines ?
It controls the piston position for cut off of steam, for release of steam and compression position for steam in cylinder.

95. What is the purpose of Corliss valve in place of D’-slide valve in steam engine ?
Corliss valve reduces condensation, provides independent control on admission, cut off, release and compression, and reduces driving power requirements.

96. On what factor the size of cam depends ?
Size of cam depends on base circle.

97. If base circle diameter of cam increases, what happens to pressure angle ?
It decreases.

98. If angular speed of cam is increased two times, how much jerk will be increased ?
Eight times.

99. Define primary and secondary transducers ?
A primary transducer senses a physical phenomena and converts it to an analogous output.
The analogous output is then converted into an electrical signal by secondary transducer.

100. What is the relationship between (i) axes of spin, precession, and applied gyroscopic torque and (ii) in between their planes ?
The axes of spin, precession, and applied gyroscopic torque are contained in two planes perpendicular to each other, and planes of spin, precession, and applied gyroscopic torque in the three planes perpendicular to one another.

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