Answer Happy

12. A skater with her arms stretched out is rotating about a vertical axis with an angular velocity, 0 = 6 rad/s. She pulls her arms towards the axis to decrease her rotational inertia from I= 4 kg-m² to l' = 2 kg-m². With what angular velocity o' she is rotating after pulling her arms towards the axis? (Hint: Use conservation of angular momentum). Does her rotational kinetic energy decrease or increase, account the difference. 13. The sphere starts from rest and rolls down the incline. (a) Find the velocity of its center of mass at the bottom of the incline, by using Newton's method and conservation of energy. (b) Solve the problem for rolling cylinder. Isphere (2/5) MR2, Leylid = (1/2) MR? 14. A string is wound around the disk of radius R and mass M. The disk is released from rest. (a) Find the tension in the string and the acceleration of the center of mass of the disk. (b) Find the speed of the center of mass after it falls a distance h. Answrs: T = (1/3) mg, a = 2g/3, v = (4gh/3)2