mechanics of machines two marks

8/13/2019 Mechanics of Machines Two Marks

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NOORUL ISLAM COLLEGE OF ENGINEERING

KUMARAKOIL

DEPARTMENT OF AERONAUTICAL ENGINEERING

AE 1253 - MECHANICS OF MACHINES

2 MARKS

UNIT - I1. Define a kinematics link

Each parts of a machine, which moves relative to some other part is known as

kinematics link or element.

2. What are the characteristic of a link?

It should have relative motion. It must be a resistant body.

3. What are the types of links?

Rigid link,

Flexible link,

Fluid link

4. Define a structure?

It is an assemblage of a number of resistant known as member having no relative

motion between them and meant for carrying loads having straining action.

Example: Railway Bridge, truss.

5. What is higher pair?

When the two element of a pair have a line or point contact when the relative

motion takes place and the motion between the two elements is partly turning and

partly sliding, then the pair is known as higher pair.

6. Define kinematic chain.

When the kinematics pair is coupled in such a way that the last link is jointed tothe first link to transmit definite motion it is called a kinematic chain.

7. Define kinematic pair.

The two links or elements of a machine when in contact with each other are said

to form a pair. If the relative motion between them is completely or successfully

constrained the pair is known as kinematic pair.


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8. Define mechanism.

When the one of the links of a kinematic chain is fixed the chain is known as

mechanism.

9. State Grublers criterion for plane mechanism?

Grublers criterion applies to mechanism with only single degree of freedom joint

where are overall mobility of the mechanism is unity.

3l-2j-4=0

10. Define inversion of the mechanism.

The method of obtaining different mechanism by fixing different links in a

kinematic chain is known as inversion of the mechanism.

11. What are the types of kinematic chain?

Four bar chain or quadric cyclic chain, Single slider crank chain, Double slider

crank chain

12. What is single cylinder crank chain?

Single cylinder crank chain is a modification of the basic four bar chain. It

consists of one sliding pair and three turning pairs. It is usually found in reciprocating

steam engine. It converts rotary motion in to reciprocating motion and vice versa.

13. What are the following three inversion of double slider crank chain?

Elliptical trammels,

Scotch yoke mechanism,

Oldhams coupling

14. What are the methods for determining the velocity of a point on a link?

Instantaneous centre method,

Relative velocity method

15. State D-Alemberts principle

It start that the resultant force acting on a body together with the reversed

effective force are in equilibrium.

16. State Grashofs law for a four bar mechanism.

According this law, the sum of the shortest and longest link length should not be

greater than the sum of the remaining two link length if there is to be continuous

relative motion between the two links.


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17. Define Rubbing velocity at a pin joint?

The links in amechanism are mostly connected by means of pin joints. The

rubbing velocity is defined as the algebraic sum between the angular velocities of the

two links which are connected by pin joints, multiplied by the radius of the pin. R=

w.r.

18. Name any four types of kinematics part?

Sliding pair

Turning pair

Rolling pair

Screw pair

Spherical pair

19. The Coriolis component of acceleration is taken in to account for

Quick return mechanism.

20. What is a rigid link?

A rigid link is one which does not undergo any deformation while transmitting

motion.

21. What is a belt?

The belts or ropes are used to transmit power from one shaft to another by means

of pulleys which rotates at the same speed or at different speeds.

22. What are the factors that have to be considered for the selection of a belt drive?

Speed of the driving and driven shafts.

Speed reduction ratio

Power to be transmitted

Shaft lay out

Space available

23. What are the types of belt drives?

Light drives

Medium drives

Heavy drives

24. What are the types of belt?

Flat belt


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V-belt

Circular belt or rope

25. Where is a flat belt used?

It is mostly used in the factories and workshops where a moderate amount of

power is to be transmitted from one pulley to another when two pulleys are not more

than 8 m apart.

26. Where is a V belt used?

The V belt is mostly used in the factories and workshops where a great amount of

power is to be transmitted from one pulley to another when the two pulleys are very

near to each other.

27. Define velocity ratio of a belt drive

1 1

2 2

N d

N d=

When thickness of the belt is considered

2 1

1 2

N d t

N d t

+=

+

28. Define slip of the belt

1 1

2 2

N d

N d= 1

100

S

29. What is the length of open belt drives?

L= [ ] ( )

21 2

1 2 22 4

d dd d x

x

+ + +

30. What is the length of a crossed belt drives?

L= [ ] ( )

21 2

1 2 22 4

d dd d x

x

++ + +

31. Define creep of the belt.

Tension on the two pulleys is not equal. One side, the tension is greater than the

other side due to the difference of two tensions, the belt continuously creeps over the

pulleys. This movement of the belt is very small and is called creep of belt.


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32. Define angle of contact or lap.

It is the angle subtended by the arc AB along which the belt touches the pulley at

32. What is the angle of contact for?

(a) Open belt drive

(b) Cross belt drive?

- 180

rad

+ 2 180

rad

33. What is the ratio of driving tension for flat belts?

2.3 log 1

2

TT

=

34. Define centrifugal tension in a belt.

Tc = mV2=W

gV2

35. What is the condition for the maximum power transmission?

P = (T1 T2) V

For maximum power transmission

T = 3Tc

36. What is the ratio of driving tension for V belt?

2.3 log 1

2

T

T

=

c

37. What is clutch?

A clutch is a machine member used to connect a driving shaft to a driven shaft so

that the driven shaft may be stared or stopped at with or with out stopping the driving

shaft. It is used in automobile.

38. What are the types of clutches?

Positive clutch

Friction clutch


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39. What are the types of friction clutch?

Disc or plate clutch

Cone clutch

Centrifugal clutch

40. What is a single plate clutch?

It is consist of the following parts

Driving plate

Driven plate

Pressure plate

41. What are the functions of clutch?

To engage or disengage the rest of transmission as required.

To transmit the engine power to rear wheels when the rear wheels without shock.

To enable the gear to get engaged when the vehicle is in motion.

42. What are the factors to be considered when designing a disc or plate clutch?

When there is a uniform pressure

When there is a uniform axial wear.

43. What is the formula for finding intensity of pressure?

P =( ) ( )

2 2

1 2

W

r r

44. Define average pressure Pav?

Pav= Total force on friction surface /Cross-sectional area of friction surface

45. What is the total frictional torque acting on the ring of the cone clutch?

( ) ( )

( ) ( )

3 3

1 2

2 2

1 2

2

3 n

r rT W

r r

=

46. What is bearing?

A bearing is a machine element which supports another moving machine element

known as journal. It permits a relative motion between the contact surfaces of the

member while carrying the load.

47. What are the types of bearing?

Radial bearing


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Thrust bearing

Sliding bearing

Rolling contact bearing

48. Define journal bearing or sleeve bearing?

The sliding bearing in which the sliding action is along the circumference of a

circle or an arc of a circle and carrying radial loads are known as journal or sleeve

bearings.

49. What is the thick film or hydrodynamic lubricated bearing?

The thick film bearing are those in which the working surfaces are completely

separated from each other by the lubricant. Such type of bearing are called hydrodynamic

lubricated bearing

50. What is zero film bearing?

The zero film bearing are those which operate with out any lubricant present

51. What is wedge film lubrication?

The flow of a viscous fluid in a converging channel is known as wedge film

lubrication.

52. What is squeeze film lubrication?

The resistance of a viscous fluid to being squeezed out from between approaching

surfaces known as squeeze film lubrication.

53. What are the types of rolling contact bearing?

Ball bearing

Roller bearing

54. What are types of friction clutch?

Disc clutch

Cone clutch

Centrifugal clutch

55. Mention any two advantages of V belt drive over flat belt drive.

It provides longer life 3 to 5 years

It can be easily installed and removed

High velocity ratio

Drive is positive.


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63. Define pressure angle

It is the angle between the direction of the follower motion and a normal to the

pitch curve. If the pressure angle is too large a reciprocating follower will jam in its

bearing.

64. What are the motions of the follower?

Uniform velocity

Simple harmonic motion

Uniform acceleration and retardation

Cycloidal motion

65. What are dwell periods?

The period during which the follower remains at rest are known as dwell periods.

66. Define angular velocity.

It may be defined a ratio of change of angular displacement with respect to time.

It is a vector quantity.

67. Define a gear.

A gear is a wheel provided with teeth which mesh with the teeth on another wheel

or on to rack so as to give positive transmission of motion from one component to

another.

68. What are the types of gears?

Spur gear

Helical gear

Bevel gear

Worm gear

Rack and pinion

69. Define pitch circle

It is an imaginary circle which by pure rolling action would give the same motion

as the actual gear.

70. Define pressure angle

It is the angle between the common normal to two gear teeth at the point of

contact and the common tangent at the pitch point. It is denoted by The standard

pressure angles are 141/2and 20


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71. Define Dimeteral pitch.

It is the ratio of number of teeth to the pitch circle diameter in mm

72. Define module.

It is the ratio of the pitch circle diameter in mm to the number of teeth.

73. Define arc of contact

It is the path traced by a point on the pitch circle from the beginning to the end of

engagement of a given pair of teeth.

74. State law of gearing.

The common normal at the point of contact between a pair of teeth must always

pass through the pitch point.

75. Define interference

The phenomenon when the tip of a tooth under cuts the root of its mating gear is

known as interference.

76. Define gear train

The combination of gear wheels by mean of which motion is transmitted from one

shaft to another shaft is called a gear train.

77. What are the types of gear train?

Simple gear train

Component gear train

Epicyclic gear train

78. What is simple gear train?

A simple gear train is one in which each shaft carries one wheel only. Simple gear

trains are employed where a small velocity ratio is required.

79. Define train value

It is the reciprocal of velocity ratio

=Speed of the driven No. of teeth on driver

Speed of the driver No. of teeth on driven=

80. What is a compound train?

A compound gear train is one in which each shaft carries two wheels one of

which acts as a follower and other acts as a driver to the shaft. It is used for high velocity

ratio.


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81. What are the uses of epicyclic gear train?

Transmitting high velocity ratio, with gears of moderate size in a comparatively

lesser space.

82. What are the types of vibration?

Free vibration

Force vibration

Damped vibration

83. What are the free vibrations?

Longitudinal vibration

Transverse vibration

Tensional vibration

84. What is degree of freedom?

The minimum number of independent coordinates required to specify the motion

of a system at any instant is known as degree of freedom of the system.

85. What is simple harmonic motion?

The motion of a body, to and fro a about a fixed point is called simple harmonic

motion.

86. What is critical or whirling or whipping speed?

It is the speed at which the shaft tends to vibrate violently in the transverse

direction. The critical speed of the shaft in rps is equal to the natural frequency of

transverse vibration in HZ.

87. What is force vibration?

When the body vibrates under the influence of external force then the body is said

to be under force vibration.

88. What is magnification factor?

The ratio of maximum displacement of the forced vibration to the static deflection

under static force is known as magnification factor.

89. What is frequency response curve?

A curve between magnification factor and frequency ratio ids known as is

frequency response curve.


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90. What is transmissibility?

It is defined as the ratio of the force transmitted to the force applied on the

system.

91. What is torsionally equivalent shaft?

It is the shaft which has the same torsional stiffness as that of the stepped shaft so

that it twists to the same extent under a given torque as the stepped shaft would.

92. What is single rotor system?

A shaft fixed at one end carrying a rotor at the free end, is known as single rotor

system.

93. What is node?

The point is section at which the amplitude of vibration is zero, is known as node.

94. What is two node frequencies?

One set of values given by the quadratic equation gives the position of two node

and the frequency thus obtained is known as two node frequency.

95. What is balancing?

Balancing is the process of designing or modifying machinery so that the

unbalance is reduced to an acceptable level and if possible is eliminated entirely.

96. What is mass moment?

The product of B.b or m.r is called as the mass moment.

97. What is reference plane?

Transfer the centrifugal force acting in each plane to a single parallel plane which

is termed as reference plane.

98. What is static balance?

A system is rotating masses is said to be in static balance if the combined mass

centre of the system lied on the axis of rotation.

99. What are conditions for complete balancing?

The resultant centrifugal forces must be zero

The resultant couple must be zero.

100. What is dynamic balance?

A system of rotating masses is in dynamic balance when there does not exist any

resultant centrifugal force as well as resultant couple.


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101. What are the types of locomotive?

Coupled locomotive

Uncoupled locomotive.

102. Define tractive force

The resultant unbalance force due to the two cylinders along the line of stroke is

known as tractive force.

103. What is swaying couple?

The unbalance forces acting at a distance between the line of stroke of the two

cylinders constitute a couple in the horizontal direction. This couple is known as swaying

couple.

104. Define hammer blow

The maximum magnitude of the unbalance forces along the perpendicular to the

line of stroke is known as hammer blow.

mechanics of machines two marks

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