Dynamics of Machinery: Two Mark Questions & Answers
Dynamics of Machinery: Two Mark Questions & Answers
Dynamics of Machinery: Two Mark Questions & Answers
Dynamics
of
Machinery
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SRIT Dynamics of Machinery
Force Analysis
1. Define inertia force.
Inertia force is an imaginary force, which when acts upon a rigid body, brings it to an
equilibrium position. Mathematically,
Inertia force = -Accelerating force = -m.a
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SRIT Dynamics of Machinery
The forces acting on links of a mechanism from outside are called as applied forces.
When two ware more links are connected to form a pair and hence mechanism, the
pair of action and reaction forces between any of two links are called constraint
forces.
11. What are the conditions of equilibrium for a three force member?
Conditions are:
The resultant of three forces should be zero.
The line of action of the forces must intersect at one point known as point of
concurrency.
17. Give the equation for net load on piston for a horizontal engine?
Net load on piston = Load on piston – Inertia force – Frictional resistance
Net load on piston, Fp = FL - FI - RF
18. Give the equation for net load on piston for a vertical engine?
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SRIT Dynamics of Machinery
Net load on piston = Load on piston – Inertia force – Frictional resistance + (Mass of
reciprocating parts x gravity)
Net load on piston, Fp = FL - FI - RF + mR.g
19. What are the conditions of equilibrium for a two force member?
Conditions are:
i).The forces should be of same magnitude.
ii).The forces should act along the same line but opposite in direction.
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SRIT Dynamics of Machinery
Balancing
1. 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.
3. Give the condition for balancing several rotating masses in different planes.
Conditions are:
o The resultant centrifugal force must be zero, and
o The resultant couple must be zero.
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SRIT Dynamics of Machinery
Coupled locomotive
Uncoupled locomotive
10. What are the effects due to partial balancing of reciprocating masses?
Effects are:
An unbalance force along the line of stroke which produces,
Variation in tractive force
Swaying couple
An unbalanced force perpendicular to the line of stroke which produces,
Hammer blow (variation of pressure on the rails)
15. Give the expression for primary unbalanced force acting on a piston?
Primary unbalanced force acting on a piston, FP = mω2 r cosθ
16. Give the expression for secondary unbalanced force acting on a piston?
Secondary unbalanced force acting on a piston, FR =mω2 r (cos2θ/n)
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SRIT Dynamics of Machinery
Secondary unbalanced forces are maximum when crank angle is 00, 900, 1800 and
3600.
19. Give the expression for variation of tractive force and when is it maximum?
Variation of tractive force, FT = ((1-c) mω2 r) [cosθ - sinθ ]
Tractive force is maximum when θ= 1350 and 3150
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SRIT Dynamics of Machinery
CONTROL MECHANISMS
1. What is the function of a governor?
The main function of a governor is to regulate the mean speed of an engine, when
there are variations in the load.
7. Define Stern.
The rear end of the ship is known as stern or aft.
8. Define Port
The left hand side of the ship when viewed from the stern is known as port.
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SRIT Dynamics of Machinery
18. What are the three types of movements a ship can have?
Types of movements are steering, pitching and rolling.
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SRIT Dynamics of Machinery
LONGITUDINAL VIBRATION
1. What is vibration?
When elastic bodies such as a spring, a beam, and a shaft are displaced from the
equilibrium position by the application of external forces, and then released, they
execute a vibratory motion.
8. Define frequency.
It is defined as number of cycles described in one second. It is usually expressed in
cycles per second
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SRIT Dynamics of Machinery
Vibrations which occur along the axis of the shaft or spring are known as
longitudinal vibrations. The vibrations which occur in the direction approximately
perpendicular to the axis of the shaft are known as transverse vibrations.
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SRIT Dynamics of Machinery
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SRIT Dynamics of Machinery
8. What are the assumptions made in calculating the free torsional vibrations of
a geared system?
Assumptions:
The gear teeth are rigid and are always in contact
There is no backlash in the gearing
The inertia of the shafts and gears are negligible.
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SRIT Dynamics of Machinery
14. What are the assumptions made for the supports according to the type of
bearings?
A shaft supported in short bearings is assumed to be a simply supported shaft while
the shaft supported in long bearings is assumed to have both ends fixed.
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