Question

8) Alice is standing on a rotating platform rotating counterclockwise (as viewed from above) with her arms extended, taking 3.3 seconds per revolution. In this position, her moment of inertia (plus the platform’s) equals IA = 3.2 kg m2 . a) What is her angular momentum? b) Bob throws a ball at Alice, that approaches her extended hand in a horizontal tangential direction opposite to her motion, as seen (from above) in Figure 2. If Alice’s hand is 0.81 m away from her rotational axis and the ball’s mass is mb = 0.29 kg, what should be the speed of the ball for it to stop completely Alice’s rotation when she catches it? Hint: you want the final total angular momentum to vanish.

Ball Hand Alice Figure 2: Figure for Problem 8. (The circle is Alice's head and the rectangles are her arms, viewed from above. The dotted circle is the trajectory Alice's hand follows previous to catching the ball.)

Answer 1

con angular geed W. =3.3 revis =3.3% 27 rad's Wi= 18.84 ratts 20-724 radis angular momentum l-Iwi = 3.20 20.724 L., 66.32 kg m/s using ongular momentum conservation morra Lid 0.29 xVax0.81 = 66.32 v=282.32 m/s