A ball of mass m moving with velocity v? i strikes a verticalwall as shown in (Figure 1). The angle between the ball's initialvelocity vector and the wall is ?i as shown on the diagram, whichdepicts the situation as seen from above. The duration of thecollision between the ball and the wall is ?t, and this collisionis completely elastic. Friction is negligible, so the ball does notstart spinning. In this idealized collision, the force exerted onthe ball by the wall is parallel to the x axis. What is the finalangle ?f that the ball's velocity vector makes with the negative yaxis?