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Physics

Physics. Session. Rotational Mechanics -7. Session Objectives. Session Objective. Problems. Class Test.

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Physics

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  1. Physics

  2. Session Rotational Mechanics -7

  3. Session Objectives

  4. Session Objective • Problems

  5. Class Test

  6. A wheel of mass 2 kg having practically all the mass concentrated along the circumference of a circle of radius 20 cm is rotating on its axis with an angular velocity of 100 rad/s. The rotational kinetic energy of the wheel is • 4 J (b) 70 J • (c) 400 J (d) 800 J Class Exercise - 1

  7. Solution Hence, answer is (c).

  8. A rod of length L is hinged from one end. It is brought to the horizontal position and released. The angular velocity of the rod when it is in vertical position is Class Exercise - 2

  9. Solution Loss in potential energy = Gain inkineticenergy

  10. Solution contd.. Hence, answer is (b).

  11. The moment of inertia of a square plate about one of its diagonal is (Assumeto be the side of the square and mass M) Class Exercise - 3

  12. MI of a square plate about an axispassing through itscentre andperpendicular to its plane is I0 = 2ID Solution Hence, answer is (b).

  13. A uniform disc of radius R and mass M is mounted on an axle as shown in the figure. A light cord is wrapped around the rim of the wheel and a downward pull T is exerted on the cord. The angular acceleration of the wheel is Class Exercise - 4

  14. Solution Applying torque equation,torqueof tension about O = TR Hence, answer is (a).

  15. A particle of mass m is released from rest at A, falling parallel to y-axis. The torque acting on the particle with respect to origin and angular momentum at any time with respect to origin is • mgb and mgt (b) mgt and mg • (c) mgb and mgbt (d) mgt and mgbt Class Exercise - 5

  16. Momentum = mgt Solution Angular momentum = Linear momentum × Perpendiculardistance from the axis Velocity after time t of falling = gt L = mgt × b L = mgbt … (ii) Hence, answer is (c).

  17. The ratio of the radius of gyration of a circular disc and a circular ring of the same mass and radius about a tangential axis parallel to the plane is • 6 : 5 (b) 1 : 2 • (c) 5 : 6 (d) None of these Class Exercise - 6

  18. M.I. of circular disc about tangentialaxis by theorem ofparallel axis is M.I. of ring about tangential axis by theorem of parallelaxis is Solution Hence, answer is (d).

  19. The moment of inertia of a cylinder of radius a mass M and height h about an axis parallel to the axis of the cylinder and distant b from the centre is Class Exercise - 7

  20. Solution According to theorem of parallel axis, Hence, answer is (d).

  21. Thank you

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