This document contains 16 questions and answers related to dynamics of machines. It discusses topics such as dynamic balancing, equivalent stiffness of springs, damping coefficients, Laplace transforms, noise tolerance levels, evaluating balancing machines, transmissibility ratios, acoustic impedance, the Doppler effect, representing transient vibrations, hammer blows and swaying couples, types of vibrations, shock spectra, sound propagation, and critical shaft speeds.

1. PREVIOUS YEAR SHORT QUESTIONS
AND ANSWERS
ME 010 702 DYNAMICS OF MACHINE
BINIL BABU
DEPT . OF MECHANICAL ENGINEERING
SNMIMT,MALIANKARA

2. 1. State the condition for dynamic balancing.
A body is said to be in dynamic balance the
resultant force and resultant couple acting on
the body should be zero. If a body is in
dynamic balance it automatically satisfy the
condition of static balance.

3. 2. Discuss the method to find out equivalent
stiffness
 When springs are in series
 Keq = k1+k2/k1k2
 (Draw figure)
 When springs are in series
 Keq = k1+k2+....
 (Draw figure)

4. 3. Define the term coefficient of damping and critical
damping coefficient
Damping force is proportional to velocity of the
system. Damping coefficient is the damping
force per unit velocity.
Critical damping coefficient is the value of
damping coefficient at which the system
restore its equilibrium position at the shortest
possible time.
The ratio of damping coefficient to critical
damping coefficient is known as damping
factor.

5. 4. Write a note on Laplace transform
 Laplace transform is a calculus operational
function which converts differential equation in
time domain to a new domain s (frequency
domain), which is a simple algebraic equation.
The solution in s domain obtained by solving
simple algebraic equations and then by the
process of inverse transformation, the solution
in time domain obtained.

6. 5. Discuss tolerance level of human ear in
industrial context.
 If the sound goes beyond the tolerance level,
it is classified as noise, but this depends on
the characteristics of the particular person as
well as the sound. Almost every aspect of
modern life generates noise –
industrial processes, ... Human ears respond
to frequencies between 20Hz and
20,000Hz.According to OSHA (Occupational
Safety and Health Administration)there is some
standard permissible time for human under
various noise level as given below:-

7. Sound pressure level(dB) Permissible time (hours)
80 32
85 16
90 8
100 3
110 0.5
115 0.25
120 0.125

8. 6. How will you evaluate the performance of a
balancing machine
 Balancing is the process of designing or
modifying machinery so that the unbalance is
reduced to an acceptable level and if possible
eliminate completely. Heavy machines containing
generally consists of rotating as well as
reciprocating masses, it is necessary to balance
the unbalanced forces generated by the inertia
of moving parts. The most common approach to
balancing is by redistributing the mass which
may by addition or removal of mass from
various members.

9. 7. Define transmissibility ratio
 Transmissibility is defined as the ratio force
transmitted to the foundation to the force
applied .It is the measure of the effectiveness
of the vibration isolating material.
 TR= F/ FT

10. 8. Define acoustic impedance
 Acoustic impedance is a measure of the
opposition that a system presents to the
acoustic flow resulting of an acoustic pressure
applied to the system.
 Sound travels through materials under the
influence of sound pressure. Because molecules
or atoms of a solid are bound elastically to one
another, the excess pressure results in a wave
propagating through the solid.
 The acoustic impedance (Z) of a material is
defined as the product of its density (p) and
acoustic velocity (V).

11. 9. Write a note on Doppler effect
The Doppler effect (or the Doppler shift) is the
change in frequency or wavelength of
a wave for an observer who is moving relative
to the wave source.
Eg: change of pitch heard when
a vehicle sounding a siren or horn approaches,
passes, and recedes from an observer.
Compared to the emitted frequency, the
received frequency is higher during the
approach, identical at the instant of passing
by, and lower during the recession

12. 10. How will you represent transient vibration
 Transient vibration is defined as a temporarily
sustained vibration of a mechanical system. It
may consist of forced or free vibrations, or
both. Transient loading, also known as impact,
or mechanical shock, is a non-periodic
excitation, which is characterized by a sudden
and severe application.
 In real life, mechanical shock is very common.
Some examples of shock could be a forging
hammer, an automobile passing trough a road
bump, the free drop of an item from a height,
etc.

13. 11. Explain Hammer blow and swaying couple
 Hammer blow and swaying couple are the
effect of partial balancing of locomotives.
 HAMMER BLOW: It is the maximum vertical
unbalanced force caused by the mass provided
to balance the reciprocating masses.
 SWAYING COUPLE: Unbalanced primary force
along lines of stroke are separated by a
distance “l”

14. 12. What are different types of vibrations?
Explain
 Vibration classified:-
 (i) Free vibration and forced vibration
 (ii) Damped and Un-damped vibration
 (iii) Longitudinal vibration, tranverse vibration
and torsional vibration.
 (iv) Linear and non-linear vibration.

15. 13. Explain shock spectrum
 Any mechanical system is capable of transient
vibrations in the form of motions of one part
with respect to another, and involving
resonances at a number of frequencies. The
primary effect of shock is to excite the
equipment at its resonance frequencies. This
vibration dies away depending of the amount of
damping present in the system.
 Spectrum was defined as a plot of a response
quantity (displacement, velocity or
acceleration), against the ratio of the period
or frequency of the forcing function, to the
natural period or frequency of the system.

16. 15. Explain sound propagation
Sound propagates through air as a longitudinal
wave.
The speed of elastic waves is related to two
properties of the medium: elasticity and
density. The speed, in meters per second, at
which a sound wave travels through a media is
the speed of propagation, c.

17. 16. Describe critical speed of shaft
 The speed at which the shaft runs so that the
additional deflection of the shaft from the axis
of rotation becomes infinite is known as critical
or whirling speed of shaft.
 (Draw figure.)