D A quarterback is set up to thmw the football to a receiver who is running with a constant velocity 5-}, directly away from the quarterback and is now a distance D away from the quarterback. The quarterback gures that the ball must be thrown at an angle H'to the horizontal and he estimates that the receiver must catch the ball a time interval tr, after it is thrown to avoid having opposition players prevent the receiver from making the catch. In the following you may assume that the ball is thrown and caught at the same height above the level playing eld. Assume that the y coordinate of the ball at the instant it is thrown or caught is y = l} and that the horizontal position of the quarterback is or = l}. {gure 1]