NCERT Class 11 Chapter 7 Physics Systems of Particles and Rotational Motion MCQ

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1. 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

2. 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

3. The motion of the centre of mass depends on

A. total external forces

B. total internal forces

C. None of these

D. Both

4. 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

5. In rotatory motion, linear velocities of all the particles of the body are

A. different

B. zero

C. cannot say

D. None of these

6. If the resultant of all external forces is zero, then velocity of centre of mass will be

A. zero

B. neither (a) nor (b)

C. constant

D. either (a) or (b)

7. In rotation of a rigid body about a fixed axis, every ...A...of the body moves in a ...B..., which lies in a plane ...C... to the axis and has its centre on the axis. Here, A, B and C refer to

A. particle, circle and perpendicular

B. particle perpendicular and perpendicular

C. circle, particle and perpendicular

D. particle, perpendicular and circle

8. Centre of mass of the earth and the moon system lies

A. closer to the earth

B. closer to the moon

C. at the mid-point of line joining the earth and the moon

D. cannot be predicted

9. 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

10. Assertion : The centre of mass of an isolated system has a constant velocity.
Reason : If centre of mass of an isolated system is already at rest, it remains at rest.

A. Assertion is correct, reason is correct; reason is not a correct explanation for assertion

B. Assertion is correct, reason is correct; reason is a correct explanation for assertion

C. Assertion is incorrect, reason is correct

D. Assertion is correct, reason is incorrect

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11. Concrete mixture is made by mixing cement, stone and sand in a rotating cylindrical drum. If the drum rotates too fast, the ingredients remain stuck to the wall of the drum and proper mixing of ingredients does not take place. The maximum rotational speed of the drum in revolutions per minute (rpm) to ensure proper mixing is close to : (Take the radius of the drum to be 1.25 m and its axle to be horizontal):

A. 27.0

B. 0.4

C. 1.3

D. 8.0

12. Angular velocity of each particle of a rotating rigid body about axis of rotation is

A. same

B. different

C. depends on relative position

D. None of these

13. A wheel rotates with a constant acceleration of 2.0 radian/sec2. If the wheel starts from rest, the number of revolutions it makes in the first ten seconds will be approximately

A. 16

B. 24

C. 32

D. 8

14. A wheel has a speed of 1200 revolutions per minute and is made to slow down at a rate of 4 radians/s2. The number of revolutions it makes before coming to rest is

A. 314

B. 722

C. 272

D. 143

15. When a ceiling fan is switched off, its angular velocity falls to half while it makes 36 rotations. How many more rotations will it make before coming to rest?

A. 12

B. 18

C. 36

D. 24

16. A mass is revolving in a circle which is in the plane of paper. The direction of angular acceleration is

A. upward the radius

B. towards the radius

B. tangential

D. at right angle to angular velocity

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. A couple produces

A. rotational motion

B. linear motion

C. both

D. None of these

19. 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

20. 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

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21. A particle performing uniform circular motion has angular momentum L. If its angular frequency is doubled and its kinetic energy halved, then the new angular momentum is

A. L/2

B. L/4

C. 2 L

D. 4 L

22. A car is moving with a speed of 108 km/hr on a circular path of radius 500 m. Its speed is increasing at the rate of 2 m/s. What is the acceleration of the car?

A. 9.8 m/s²

B. 2.7 m/s²

C. 3.6 m/s²

D. 1.8 m/s²

23. The moment of inertia of uniform circular disc about an axis passing its centre is 6kgm². its M.I. about an axis perpendicular to its plane and just touching the rim will be

A. 18 kg m²

B. 30 kg m²

C. 15 kg m²

D. 3 kg m²

24. A particl undergoes uniform circular motion. About which point on the plane of the circle will the angular momentum of the particle remain conserved?

A. centre of the circle

B. on the circumference of the corcle

C. inside the circle

D. outside the circle

25. Two particles A and B, initially at rest, moves towards each other under a mutual force of attraction. At the instant when the speed of A is u and the speed of B is 2 u, the speed of centre of mass is,

A. Zero

B. u

C. 1.5 u

D. 3 u