Engineering Physics Questions and Answers for Aptitude test focuses on “Moment of Inertia and its Significance”.
1. The instantaneous speed of the point of contact during rolling is zero.
a) True
b) False
Answer: a
Clarification: A rolling body can be imagined to be rolling about an axis passing through the point of contact of the body and the ground. Hence the instantaneous speed of the point of contact is zero.
2. A mass m is moving with a constant velocity along a line parallel to the x-axis, away from the origin. Its angular momentum with respect to the origin ___________
a) Is zero
b) Remains constant
c) Goes on increasing
d) Goes on decreasing
Answer: b
Clarification: Angular momentum = Mass of momentum
L = mv×h = constant
As the particle moves, m, v and h all remain unchanged.
3. A particles undergoes uniform circular motion. About which point on the plane of the circle, will the angular momentum of the particles remain conserved?
a) Centre of the circle
b) On the circumference of the circle
c) Inside the circle
d) Outside the circle
Answer: a
Clarification: In uniform circular motion, centripetal force acts towards the centre. Torque due to such a force about the centre is zero. Hence the angular momentum is conserved about the centre of the circle.
4. If the resultant of all the external forces acting on a system of particles is 0, then from an inertial frame, one can surely say that ___________
a) Linear momentum of the system does not change in time
b) Kinetic energy of the system does not change in time
c) Angular momentum of the system does not change in time
d) Potential energy of the system does not change in time
Answer: a
Clarification: According to the law of conservation of linear momentum if external force is 0 then the linear momentum of the system does not change in time. There may be external forces acting due to which kinetic energy or potential energy or both may change. Also, net force is 0 does not mean net torque is 0. So angular momentum may change. Hence only linear momentum of the system does not change in time.
5. Statement 1: If there is no external torque on the body about its centre of mass, then the velocity of the centre of mass remains constant.
Statement 2: The linear momentum of the isolated system remains constant.
a) Statements 1 and 2 are true and statement 2 is the correct explanation of statement 1
b) Statement one and two are true and statement2 is not the correct explanation of statement1
c) Statement 1 is true, statement 2 is false
d) Statement 2 is true, statement 1 is false
Answer: d
Clarification: The absence of external torque does not ensure the absence of external force. If an external force is present, then the velocity of the centre of mass will not remain constant. Thus statement 1 is false.
6. If a person standing on a rotating disc stretches out his hands, the angular speed will ___________
a) Increase
b) Decrease
c) Remains same
d) Increases and then decreases
Answer: b
Clarification: As the person stretches out his hands, his moment of inertia increases. To conserve angular momentum, his angular speed increases.
7. Analogue of mass in rotational motion is ___________
a) Moment of inertia
b) Angular momentum
c) Gyration
d) Angular acceleration