Engineering Questions with Answers - Multiple Choice Questions
Machine Dynamics MCQ– Effect of Gyroscopic Couple on a Disc Fixed Rigidly at a Certain Angle to a Rotating Shaft
1 - Question
In the figure given below, the moment of inertia about polar axis OP is _______
a) mr2/2
b) mr2
c) 2mr2
d) 4mr2
View Answer
Answer: a
Explanation: In the figure given above, if m is the mass of the disk and r is the radius, then the moment of inertia about the axis OP is given by mr2/2.
2 - Question
When seen from the top, the gyroscopic couple acting on the disc will act in the clockwise direction.
a) True
b) False
View Answer
Answer: b
Explanation: When seen from the top, the gyroscopic couple acting on the disc will act in the anti-clockwise direction.
3 - Question
In the figure given below, the moment of inertia about diametral axis is _______
a) m(l2/12 + r2/4)
b) m(l2/6 + r2/4)
c) m(l2/12 + r2/2)
d) m(l2/12 + r2)
View Answer
Answer: a
Explanation: If m is the mass, l is the length and r is the radius of the disc, then the moment of inertia about the diametral axis is given by m(l2/12 + r2/4).
4 - Question
If the length of the disc is negligible, then what will be the moment of inertia about the diametral axis?
a) mr2/4
b) mr2
c) mr2/2
d) 2mr2
View Answer
Answer: a
Explanation: If m is the mass, l is the length and r is the radius of the disc, then the moment of inertia about the diametral axis is given by m (l2/12 + r2/4), if l is negligible then the expression becomes
mr2/4.
5 - Question
If the length and radius of the disc is same them moment of inertia is more about which axis?
a) Polar
b) Diametral
c) Shaft
d) Center
View Answer
Answer: a
Explanation: If the length and radius are same then the moment of inertia will be more about the polar axis. Mr2/2 as compared to mr2/3.
6 - Question
From the following data calculate the gyroscopic couple on the bearing in N-m.
Mass of disc = 30 Kg, diameter = 60 cm
Rotation speed = 1200 rpm
Angle between disc and a plane 90 degree to the axis of shaft = 1°
a) 180
b) 186
c) 190
d) 196
View Answer
Answer: b
Explanation: ω = 125.7 rad/s
Couple acting on the bearings
= mω2r2/8 sin2θ
substituting the values we get
C = 186 N-m.
7 - Question
If the rotation speed of the disc is increased to 2 times and the mass is reduced to half, overall the Couple acting on bearings will increase.
a) True
b) False
View Answer
Answer: a
Explanation: If the rotation speed of the disc is increased to 2 times and the mass is reduced to half, overall the Couple acting on bearings will increase as couple on bearing depends on the relation
mω2r2/8 sin2θ, hence it will increase by two times.