CBSE Class 12 Physics Rotational Motion Assignment

CBSE Class 12 Physics Rotational Motion Assignment. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Comprehension-1

To start rolling, a torque about centre of the body is required, which is usually provided by friction or any other external force acting on the body. When a body rolls on the rough ground, friction does not work over it. In the given figure a ball is released from rest which rolls down on inclined surface and movesup on the other side.

First half of the track is rough enough to support rolling and the other half is smooth. Now
answer the following questions.
1. The velocity of sphere on point B is
(a) 2gh (b) gh710(c) gh (d) none of these

2. The sphere reaches the other side up to point H. Where H is
(a) h (b) 57h (c) 75h (d) none of these

3. In the above question, the correct statement is
(a) the ball will roll from A to B and onward.
(b) the ball will reach at point C where its K.E. is zero
(c) the ball will reach up to point C and its K.E. at highest point will not be zero.
(d) none of them is correct

Comprehension-2
As in linear motion, External force changes the linear momentum similarly in rotational motion external torque changes the angular momentum and relationship between torque and angular momentum (L)

5. Change in linear momentum of cylinder is
(a) FΔt (b) 2 FΔt (c) F/2 Δt (d) none of these

6. Change in translational kinetic energy of cylinder is
(a) F² Δt ² /2m  (b) 1/2 mVc² (c)  m/4 V²c (d) 1/4 mr ²ω²

7. Change in angular velocity is
(a) Vc/r (b) F Δt/mr  (c) 2 F Δt/ mr (d) none of these

Each of the questions given below consists of two statements, an assertion (A) and reason (R).
Select the number corresponding to the appropriate alternative as follows
(a) If both A and R are true and R is the correct explanation of A
(b) If both A and R are true but R is not the correct explanation of A
(c) If A is true but R is false
(d) If A is false but R is true

8. A: When a disc is rolling down an inclined plane without slipping, friction acts up the plane.
R: Friction always supports rolling

9. A: For a system of particles under central force field, the total angular momentum is conserved.
R: The torque acting on such a system is zero.

10. A: If a reel of thread is allowed to enroll vertically under its own weight, then its acceleration is (2/3)g.
R: a = (g sin θ)/(1 + K²/R²)

11. A. Moment of inertia is a scalar quantity
R. The value of the moment of inertia of a body about a given axis remains unchanged even though the direction of rotation about the axis is reversed.

12. A. A wheel rotating at a constant angular velocity ω, about a fixed axis, is in mechanical equilibrium.
R. Accelerations acting on particles on opposite directions are equal but in opposite directions. So, the resultant acceleration on wheel is zero.

13. A. A body moving in a circular path with fixed speed is not in equilibrium.
R. No torque acts on it, but resultant force acting on it is not zero.

14.. A. When a particle is moving uniformly in a circular path, it is in rotational equilibrium.
R. In this case, no torque acts on it.

15. A. Torque acting on a body due to centripetal force responsible for rotating body in a circular path, is zero
R. When two parallel forces, equal in magnitude but opposite in directions, act on a body, then these produce a torque.

16. A. Rotational K.E. of a diver, turning somersaults before striking water, increases.
R. Moment of inertia of the body of the diver decreases, when he pulls the parts of his body inwards to produce somersaults.

17. A. When a solid sphere of a larger radius and another solid sphere of smaller radius, both of same material, are just released from same position of the same inclined plane, both reach the bottom of the inclined plane in the same time.
R. Moment of inertia of larger sphere is larger than that of smaller one.

18. A. A cyclist always bends inwards while negotiating a curve.
R. By bending he lowers his centre of gravity.

19. A. In case of rotational motion, centre of mass and centre of gyration of a rigid body never coincide, except for a point mass.
R. Centre of gyration depends on the distribution of particles about the axis of rotation, whereas centre of mass of a rigid is fixed with respect to its geometry.

20. A. Frictional force is used for stopping rotational motion as well as for producing rotational motion of a body. So the direction of frictional force acting on a body may change, depending on its requirement.
R. Frictional force always opposes the motion of a body.

21. A. Angular momentum and mechanical energy of any particle moving under the influence of gravitational force are conserved.
R. Gravitational force is a nonconservative for

Miscellaneous Assignment
1. (b)   2. (c)   3.(c)   4. (b)  5. (a)  6. (a) 7. (c) 8. (a)   9. (a) 10. (b)  11. (b) 12. (a) 13. (a) 14. (a) 15. (b) 16. (b) 17. (b) 18. (a) 19. (c) 20. (c)