Halliday, Resnick & Walker — Motion in Two and Three Dimensions: Problem 72

A rugby player runs with the ball directly toward his opponent’s goal, along the positive direction of an x axis. He can legally pass the ball to a teammate as long as the ball’s velocity relative to the field does not have a positive x component. Suppose the player runs at speed 4.0 m/s relative to the field while he passes the ball with velocity \(\vec{v}_{BP}\) relative to himself. If \(\vec{v}_{BP}\) has magnitude 6.0 m/s, what is the smallest angle it can have for the pass to be legal?