Engineering Questions with Answers - Multiple Choice Questions
Machine Dynamics MCQ – Coefficient of Fluctuation of Speed
1 - Question
Coefficient of fluctuation is the ratio of ______
a) The maximum fluctuation of speed to the mean speed
b) The minimum fluctuation of speed to the mean speed
c) The maximum speed to the mean speed
d) The minimum speed to the maximum speed
View Answer
Answer: a
Explanation: Maximum fluctuation of speed is defined as the difference between the maximum and minimum speeds during a cycle. The ratio of the maximum fluctuation of speed to the mean speed is known as the coefficient of fluctuation of speed.
2 - Question
Coefficient of steadiness is reciprocal of coefficient of fluctuation of speed.
a) True
b) False
View Answer
Answer: a
Explanation: Coefficient of steadiness is defined as the ratio of mean speed to the ratio of maximum fluctuation of speed, hence it is the reciprocal of coefficient of fluctuation of speed.
3 - Question
If the minimum speed of the engine is half the maximum speed, then coefficient of fluctuation is _____
a) 0.5
b) 1.5
c) 2
d) 0.66
View Answer
Answer: d
Explanation: Let N be the maximum speed, then minimum speed is N/2
mean speed = (N+N/2)/2 = 3N/4
Maximum fluctuation = N – N/2 = N/2
therefore coefficient of fluctuation = 2/3 = 0.66.
4 - Question
If the mean speed is 3/4th of the maximum speed, the coefficient of steadiness is ______
a) 4/3
b) 3/2
c) 3/4
d) 1
View Answer
Answer: b
Explanation: Let N be the mean speed and N1 and N2 be the maximum and minimum speed respectively,
given N=3N1/4 , N1 = 4N/3
also N = (N1+N2)/2
N = 2N/3 + N2/2 : N2 = 2N/3
maximum fluctuation = N1– N2 = 4N/3 – 2N/3 = 2N/3
mean speed = N
therefore coefficient of steadiness = N/(2N/3)
= 3/2.
5 - Question
The moment of inertia of a flywheel is 6500 kg-m2, from the turning moment diagram, it is found that fluctuation of energy is 56000 N-m, if mean speed is 120 rpm, then find maximum speed.
a) 121
b) 119
c) 122
d)118
View Answer
Answer: a
Explanation: We know that ΔE= I ω2. Cs
= I ω. (ω1-ω2)
= 6500. 120x(2π/60)2( N1– N2)
N1– N2 = 2
N=120
Therefore, N1=121.
6 - Question
The moment of inertia of a flywheel is 6500 kg-m2, from the turning moment diagram, it is found that fluctuation of energy is 56000 N-m, if mean speed is 120 rpm, find the minimum speed.
a) 121
b) 119
c) 122
d) 118
View Answer
Answer: b
Explanation: We know that ΔE = I ω2. Cs
= I ω. (ω1-ω2)
= 6500. 120x(2π/60)2(N1– N2)
N1– N2 = 2
N=120
Therefore, N2=119.
7 - Question
In order to reduce the heavy weight of the flywheel which of the following mechanical component is used?
a) Bearings
b) Shaft
c) Gears
d) Engine
View Answer
Answer: c
Explanation: The mass of the flywheel depends on the velocity at which it rotates, the velocity can be moderated by installing a set of gears. This results in reduction of mass of flywheel.
8 - Question
The main function of a flywheel is to cause variations in the speed of a shaft caused by torque fluctuations.
a) True
b) False
View Answer
Answer: b
Explanation: The primary function of a fly wheel is to smoothen out variations in the speed of a shaft caused by torque fluctuations, this is basically to lessen the fluctuations of the torque. If the source of the driving torque or load torque is fluctuating in nature, then a flywheel is used.
9 - Question
When the flywheel absorbs energy, its speed ________
a) Remains unaffected
b) Increases
c) Decreases
d) Goes down to 0
View Answer
Answer: b
Explanation: When a flywheel absorbs energy, its speed increases and when it gives up energy, its speed decreases. This effect is reflected in the turning moment diagram of the flywheel.