Chapter 9, Problem 71GP

* Superball If you give a superball backspin and throw it toward a horizontal floor, it is possible that the ball bounces backward, as shown in Figure P9.71. If the ball has a color pattern or stripes, you may also notice that during the collision with the ground, the direction of rotation of the ball changes, as indicated in the figure. Both changes (the change of the ball’s translational velocity and the change of the balls angular velocity) are the result of a force exerted on the ball by the ground during the collision. (a) In which approximate direction did the ground exert the force on the ball in the case shown in the figure? Choose the best answer from the options given in the figure and explain your answer. (b) The ball has initial and final velocity (with components $v_{x\text{i}},v_{y\text{i}}$ and $v_{x\text{f}},v_{y\text{f}}$) and initial and final angular velocity ( ${\omega }_{\text{i}}\text{and}{\omega }_{\text{f}}$). During the collision, the ground exerts a force (determined by $F_z$ and $F_y$) on the ball. Complete the table below by drawing crosses in the cells that correctly connect changes of the quantities in the first column and the components of the force during the collision. Explain your answers.

	Fx	Fy
$v_{x\text{f}}-v_{x\text{i}}$
$v_{y\text{f}}-v_{y\text{i}}$
${\omega }_{\text{f}}-{\omega }_{\text{i}}$