1. Physics

2. Session Rotational Mechanics - 1

3. Session Opener Earth rotates about its own axis in one day. Have you ever wondered what will happen to the length of a day if all the sea-water was to evaporate?

4. Session Objectives

5. Session Objective 1.Definitions of Angular Velocity & Acceleration(Instantaneous/Average) 2.Rotational Kinematics Equations 3.Relation between angular and Linear Quantities

6. Angular Displacement It is the angle turned by a body or particle about a given axis of rotation It is dimensionless Unit: Radians

7. Angular velocity Instantaneous angular Velocity Average angular Velocity Unit : rad/s

8. Angular acceleration Instantaneous angular acceleration: Average angular acceleration: Unit : rad/s 2

9. LINEARANGULAR Displacement Velocity Acceleration Linear and Angular Variables

10. O x y v r S P atat arar a Relationship Between Angular and Linear quantities

11. O x y O a x y t=0 x=x 0 v0v0 t=t x=x 1 v1v1 Rotational Kinematics Equations a is constant  is constant

12. Class Test

13. Class Exercise - 1 The length of the seconds hand of a clock is 10 cm. The speed of the tip of the hand is Solution : Hence Answer is (c)

14. Class Exercise - 2 A body of mass 100 g revolves in a circle on a horizontal frictionless table attached by a cord 21 cm long to a pin set on the surface. If the body makes 2 complete revolutions per second, find the force exerted on it by the chord. (a)3.23 N(b) 3.40 N (c) 3.38 N(d) 3.32 N Solution : Hence Answer is (d)

15. Class Exercise - 3 A motor car is traveling at 30 m/s on a circular road of radius 500 m. It is increasing in speed at a rate of 2 m/s 2. What is its acceleration? v = 30 m/s, r = 500 m, a t = 2 m/s Solution :

16. Class Exercise - 4 A constant torque is acting on a wheel. If starting from rest the wheel makes n rotations in t seconds, the angular acceleration is given by:

17. Solution Hence answer is (a)

18. Class Exercise - 5 We know, at t = 5s Solution : Hence answer is (b) A particle starts rotating from rest according to the formula. The angular velocity at the end of 5 seconds is (a)7.8 rad/s(b) 7.92 rad/s (c) 7.5 rad/s(d) 9.72 rad/s

19. Class Exercise - 6 In the previous question the angular acceleration of the particle at the end of 5s will be (a)3.38 rad/s 2 (b) 8.38 rad/s 2 (c) 8.33 rad/s 2 (d) 3.83 rad/s 2 Solution : Hence answer is (d)

20. Class Exercise - 7 A flywheel rotating at the rate of 120 rpm slows down to rest at a constant rate of 2 rad/s 2. How many rotations does it make in the process?

21. Solution Hence answer is (d)

22. Class Exercise - 8 A flywheel is rotated at a speed of 60 rad/s. Because of friction on the axle, it comes to rest in 5 minutes. The angular retardation is (a) 0.3 rad/s 2 (b) 2 rad/s 2 (c) 3 rad/s 2 (d) 0.2 rad/s 2 Solution : Hence answer is (d)

23. Class Exercise - 9 A wheel rotating at a speed of 600 rpm about its axis is brought to rest by applying a constant torque for 10 seconds. The angular velocity after 5 seconds is

24. Solution Hence answer is (a) Angular velocity after 5 s is given by

25. Class Exercise - 10 A wheel is subjected to uniform angular acceleration about its axis. Initially its angular velocity is zero. In the first 2 s, it rotates through an angle  1, in the next 2s it rotates through an angle  2. The ratio of is (a)1(b) 2 (c) 3(d) 5

26. Solution Hence answer is (c)

27. Thank you