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Class 11 Physics MCQ Questions of System of Particles and Rotational Motion with Answers?

Answer 1

These MCQ Questions for Class 11 Physics with Answers were made utilizing the latest syllabus and exam pattern. We have included Class 11 Physics MCQ Questions with Answers to help students completely understand the concept. By solving these MCQ Questions once subsequent to finishing each topic for the exam, we are prepared to attempt Board and competitive exams effectively and attempt approx all Questions in the final, most important exams.

Class 11 Physics MCQ Questions of System of Particles and Rotational Motion with Answer are accessible here. You can begin practice with MCQ Question for class 11 with Answers for Board Exams.

Practice MCQ Questions for class 11 Physics Chapter-Wise

1.  A body of M.I. 3 kg m² rotating with an angular velocity 2 rad/s has the same K.E. as a mass of 12 kg moving with a velocity of

(a) 1 m/s
(b) 2 m/s
(c) 4 m/s
(d) 8 m/s

2. A thin uniform circular ring is rolling down an inclined plane of induction 30° without slipping, its linear acceleration along the inclined plane will be

(a) 2/3g
(b) g/3
(c) g/4
(d) g/2

3.  If a body is rotating about an axis, passing through its centre of mass then its angular momentum is directed along its

(a) Radius
(b) Tangent
(c) Circumference
(d) Axis of rotation

4. Moment of inertia depends on

(a) Distribution of particles
(b) Mass
(c) Position of axis of rotation
(d) All of these

5. SI unit of Centre of mass

(a) Kg
(b) M/s
(c) N
(d) J

6. A solid sphere is rotating in free space. If the radius of the sphere is increased keeping mass same, which one of the following will not be affected?

(a) Moment of inertia
(b) Angular momentum
(c) Angular velocity
(d) Rotational kinetic energy

7. A particle moves on a circular path with decreasing speed. Choose the correct statement.

(a) Angular momentum remains constant.
(b) Particle moves in a spiral path with decreasing radius.
(c) The direction of angular momentum remains constant
(d) Both b and c

8. If I,a and t are the moment of inertia, angular acceleration and torque respectively of a body rotating about any axis with angular velocity ω, then

(a)  t = Ia
(b) t = Iω
(c) I = tω
(d) a = Iω

9. The centre of mass of a body

(a) lies always on the surface of the body
(b) lies always inside the body
(c) may lie within, outside on the surface of the body
(d) lies always outside the body

10. The position of centre of mass of a system of particles does not depend upon the

(a) relative distance between the particles
(b) position of the particles
(c) symmetry of the body
(d) mass of particles

11.  The motion of the centre of mass depends on

(a) total external forces
(b) total internal forces
(c) None of these
(d) Both

12. The centre of mass of two particles lies on the line

(a) joining the particles
(b) perpendicular to the line joining the particles
(c) at any angle to this line
(d) None of these

13. A rigid body is in pure rotation, that is, undergoing fixed axis rotation. Then which of the following statement(s) are true?

(a) You can find two points in the body in a plane perpendicular to the axis of rotation having the same velocity
(b) You can find two points in the body in a plane perpendicular to the axis of rotation having the same acceleration.
(c) Speed of all the particles lying on the curved surface of a cylinder whose axis coincides with the axis of rotation is the same.
(d) Both b and c

14. A stick is thrown in the air and lands on the ground at some distance from the thrower. The centre of mass of the stick will move along a parabolic path

(a) in all cases
(b) only if the stick is uniform
(c) only if the stick has linear motion but no rotational motion
(d) only if the stick has a shape such that its centre of mass is located at some point on it and not outside it

15. A couple produces

(a) rotational motion
(b) linear motion
(c) both
(d) None of these

16. Which of the following statements about angular momentum is correct?

(a) It is directly proportional to moment of inertia
(b) It is a scalar quantity
(c) both
(d) None of these

17. Which component of force contributes to the torque?

(a) Transverse component
(b) Either radial or transverse
(c) Radial component
(d) None of these

18. The wide handle of screw is based upon

(a) turning moment of force
(b) None of these
(c) law of conservation of linear momentum
(d) upon

19. A horizontal platform is rotating with uniform angular velocity around the vertical axis passing through its centre. At some instant of time a viscous fluid of mass 'm' is dropped at the centre and is allowed to spread out and finally fall. The angular velocity during this period

(a) Decreases continuously
(b) Decreases initially and increases again
(c) Remains unaltered
(d) Increases continuously

20. A man is sitting on a rotating table with his arms stretched outwards.  When he suddenly folds his arms inside, then

(a) his angular velocity will decrease
(b) his angular velocity remains constant
(c) his moment of inertia decreases
(d) angular momentum increases

21. Assertion: The speed of whirlwind in a tornado is alarmingly high.

Reason: If no external torque acts on a body, its angular velocity remains conserved.

(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(c) If the assertion is true but the reason is false
(d) If both the assertion and reason are false

22. In an orbital motion, the angular momentum vector is

(a) Along the radius vector
(b) Parallel to the linear momentum
(c) In the orbital plane
(d) Perpendicular to the orbital plane

23. Moment of inertia of an object does not depend upon

(a) mass of object
(b) mass distribution
(c) angular velocity
(d) axis of rotation

24. If a gymnast, sitting on a rotating stool, with his arms outstretched, suddenly lowers his hands

(a) the angular velocity increases
(b)  his moment of inertia increases
(c) the angular velocity stays constant
(d) the angular momentum increases

25. A ball hits the floor and rebounds after an inelastic collision. In this case

(a) the momentum of the ball just after the collision is the same as that just before the collision
(b) the mechanical energy of the ball remains the same in the collision
(c) the total momentum of the ball and the earth is conserved
(d) the total energy of the ball and the earth is conserved

Answer 2

1.  Answer: (a) 1 m/s

Explanation: The velocity is given as,

\(\frac{1}{2}\omega^2=\frac{1}{2}mv^2\)

\(\frac{1}{2}\times3(2)^2=\frac{1}{2}\times12\times v^2\)

v = 1 m/s

2. Answer: (c) g/4

Explanation: \(a=\frac{gsin\theta}{1+\frac{k^2}{R^2}}\)

= g sin 30° / 1+ 1

= \(\frac{g}{2}\times\frac{1}{2}\)

= g/4

3. Answer: (d) Axis of rotation

Explanation: When a mass is rotating in a plane about a fixed point, its angular momentum is directed along the axis of rotation.

4. Answer: (d) All of these

Explanation: Moment of inertia of a body depends on the mass of the body, its shape and size, distribution of mass about the axis of rotation, and the position and orientation of the axis of rotation.

5. Answer: (a) Kg

Explanation: The SI Unit of mass is Kilogram(Kg) and the CGS unit is gram(g).

6. Answer: (b) Angular momentum remains constant

Explanation: Angular momentum will remain the same since external torque is zero.

7. Answer: (d) Both b and c

Explanation: Particle moves in a spiral path with decreasing radius. The directon of angular momentum remains constant.

8.Answer: (a)  t = Ia

Explanation: Torque = Product of MOI \(\times\) Ratio of change of ω

∴ t = Ia

9. Answer: (c) may lie within, outside on the surface of the body

Explanation: The position of centre of mass depend upon (1) its shape and (2) the way mass distributed on its shape. These two factor decide whether centre of mass of gravity lie inside the body or outside the body.If the solid body has a regular structure and its mass is distributed uniformly over its body (i.e. for symmetrical objects) then its centre of gravity must lie inside the body.But if solid body have irregular structure and mass is not distributed uniformly then centre of mass may lie inside the body or may outside the body.

10. Answer: (a) relative distance between the particles

Explanation: The resultant of all forces, on any system of particles, is zero. Therefore their centre of mass does not depend upon the forces acting on the particles.

11. Answer: (a) total external forces

Explanation: The motion of centre of mass depends only on the net external force. 

 F_external = Ma_CM

12. Answer: (a) joining the particles

Explanation: Centre of mass lies on the line joining the centre of masses.

13. Answer: (d) Both b and c

Explanation: In the fixed axis rotation we see that every point on the body has two components of velocity, one in the radial direction and on in the tangential direction. The resultant of these velocities is not same for any two points lying in the plane of the body. Any two points on the radial line have the radial acceleration directed towards the center of equal magnitude and the the tangential acceleration of equal magnitude as well. Thus option B is correct. All the particles lying on the curved surface of a cylinder whose axis coincides with the axis of rotation have the same speed but different velocities.

14. Answer: (a) in all cases

Explanation: The motion of centre of mass of the body depends only on external forces.Thus COM of the stick will move along a parabolic path in all cases .

15. Answer: (a) rotational motion

Explanation: A couple mainly comprises of two parallel forces which are both equal and opposite. There is no line of action and hence it produces only rotational motion.

16. Answer: (a) It is directly proportional to moment of inertia

Explanation: From L = Iω, we find that angular momentum is directly proportional to the moment of inertia. Moreover, angular momentum is a vector quantity.

17. Answer: (a) Transverse component

Explanation: The radial component of the force has no contribution to the torque because it passes through the pivot point. So, it is only the tangential component of the force which affects torque (since it is perpendicular to the line between the point of action of the force and the pivot point).

18. Answer: (a) turning moment of force

Explanation: Turning moment of a force= force x distance(r) from the axis of rotation. To produce a given turning moment, force required is smaller, when r is large. That’s what happens when handle of a screw is made wide.

19. Answer: (b) Decreases initially and increases again

Explanation: According to Law of conservation of angular momentum gives

Iω = constant

When viscous liquid dropped at the center of horizontal table is made to spread out, then its moment of inertia increases and so, from Equation its angular velocity decreases. But when it starts falling then its moment of inertia starts decreasing and so, its angular velocity increases.

20. Answer: (c) his moment of inertia decreases

Explanation: According to conservation of Angular Momentum, Iω = constant
Hence, when a person sitting on a rotating stool suddenly  lowers his hands, then his angular velocity will increase and moment of inertia will decrease. 

21. Answer: (c) his moment of inertia decreases

Explanation: In a whirlwind in a tornado, the air from nearby regions gets concentrated in a small space thereby decreasing the value of its moment of inertia considerably. Since, Iω = constant, so due to decrease in moment of inertia of the air, its angular speed increases to a high value.

22. Answer: (c) If the assertion is true but the reason is false

Explanation: In orbital motion, the angular momentum vector is perpendicular to the plane in which the rotational motion take place and its sense is given by the right hand fist rule. When the fingers of right hand fist point in the direction of motion, the thumb is in the direction of  L (angular momentum).

23. Answer: (c) angular velocity

Explanation: Moment of inertia of a body does not depend on the angular velocity of the body.

24. Answer: (a) the angular velocity increases

Explanation: As the gymnast lowers his hands, the radius of gyration decreases and hence moment of inertia also decreases. Angular momentum remains conserved and hence angular velocity increases.

25. Answer: (c) the total momentum of the ball and the earth is conserved

Explanation: Momentum of the system changes only due to external force (OR impulse).
When a ball hits the floor and gets rebound, then no external force (Impulse) acts on the ball as well as the floor, thus total momentum of the "ball + earth" system remains conserved. Also some of the mechanical energy of the ball is always lost in an inelastic collision due to its deformation, hence it cannot remain conserved in this collision.

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