1 2. Angular momentum of tetherball. The object of the game tetherball (Fig. 6.24) is to hit the ball hard enough and fast enough to wind its tether cord in one direction about the vertical post to which it is tied before the opposing player can wind it in the opposite direction. The game is exciting, and the dynamics of the ball's motion are complicated. Let us examine a simple type of motion in which the ball moves in a horizontal plane in a spiral of decreasing radius as the cord winds round the post after a single blow that gives the ball an initial speed 1:0 , The length of the cord is I and the radius of the post is a « I. (a) vVhat is the instantaneous center of revolution? (b) Is there a torque about the axis through the center of the post? Is angular momentum conserved? (c) Assume that kinetic energy is conserved and calculate the speed as a function of time. (el) vVhat is the angular velocity after the ball has made five complete revolutions? Ans. w = (l - 1O'7Ta)1:0/[a2 + (l - lO'7Ta?].
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closed as too localized by David Zaslavsky♦ Jan 8 at 0:19
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