This set of Machine Dynamics Multiple Choice Questions & Answers (MCQs) focuses on “Damping Factor & Magnification Factor”.
1. The ratio of the actual damping coefficient (c) to the critical damping coefficient (cc ) is known as _________
a) Damping factor
b) Damping coefficient
c) Resistive factor
d) Resistive coefficient
View Answer
Explanation: The ratio of the actual damping coefficient (c) to the critical damping coefficient (cc) is known as damping factor or damping ratio given by c/Cc.
2. Calculate critical damping coefficient in Ns/m from the following data.
mass = 200Kg
ω = 20rad/s
a) 25,132
b) 26,132
c) 27,132
d) Not possible
View Answer
Explanation: We know that critical damping coefficient is given by the relation
Cc = 2πxmxω
inserting the values we get
Cc = 25132 N/m/s
The above value is in N/m/s and damping factor cannot be calculated in Ns/m.
3. Calculate critical damping coefficient in N/m/s from the following data:
mass = 100Kg
ω = 40rad/s
a) 25,132
b) 26,132
c) 27,132
d) 28,132
View Answer
Explanation: We know that critical damping coefficient is given by the relation
Cc = 2πxmxω
inserting the values we get
Cc = 25132 N/m/s.
4. Calculate critical damping coefficient in N/m/s from the following data:
mass = 100Kg
ω = 10rad/s
a) 5,132
b) 6,283
c) 7,132
d) 8,132
View Answer
Explanation: We know that critical damping coefficient is given by the relation
Cc = 2πxmxω
inserting the values we get
Cc = 6283 N/m/s.
5. Calculate damping ratio from the following data:
mass = 200Kg
ω = 20rad/s
damping coefficient = 800 N/m/s
a) 0.03
b) 0.04
c) 0.05
d) 0.06
View Answer
Explanation: We know that critical damping coefficient is given by the relation
Cc = 2πxmxω
inserting the values we get
Cc = 25132 N/m/s
ratio = 800/25132.
6. Calculate damping ratio from the following data:
mass = 200Kg
ω = 20rad/s
damping coefficient = 1000 N/m/s
a) 0.03
b) 0.04
c) 0.05
d) 0.06
View Answer
Explanation: We know that critical damping coefficient is given by the relation:
Cc = 2πxmxω
inserting the values we get
Cc = 25132 N/m/s
ratio = 1000/25132 = 0.04.
7. Unit of damping factor is N/m/s.
a) True
b) False
View Answer
Explanation: Damping factor is a ratio of damping coefficient to the critical damping coefficient hence, it has no unit and is a dimensionless quantity.
8. Magnification factor is the ratio of the maximum displacement due to forced vibrations to the deflection due to _______
a) Static force
b) Dynamic force
c) Torsion
d) Compression
View Answer
Explanation: Magnification factor or the Dynamic magnifier is the ratio of maximum displacement of the forced vibration to the deflection due to the static force.
9. Maximum displacement due to forced vibration is dependent on deflection due to static force.
a) True
b) False
View Answer
Explanation: Maximum displacement due to forced vibration is directly proportional to the displacement due to static force, hence it is dependent on deflection due to static force.
10. In which of the cases the factor c = 0?
a) When there is damping
b) No damping
c) Resonance
d) c is never 0
View Answer
Explanation: When there is no damping, the factor c becomes 0 and magnification factor becomes independent of the damping coefficient.
11. A body of mass 20 kg is suspended from a spring which deflects 20mm under this load. Calculate the frequency of free vibrations in Hz.
a) 3.5
b) 5
c) 6
d) 7
View Answer
Explanation: Frequency of free vibrations is given by (1/2π)√(g/d)
substituting the value, we get
f = 3.5 Hz.
12. If the mass increases, then the frequency of the free vibrations increases.
a) True
b) False
View Answer
Explanation: Frequency of free vibrations is given by (1/2π)√(g/d), from the given formula it is evident that it is independent of mass, Hence the given statement is false.
Sanfoundry Global Education & Learning Series – Machine Dynamics.
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