Figure 9-47 (attatched) shows a 0.165 kg cue ball as it bounces from the rail of a pool table. The ball's initial speed is 1.60 m/s, and the angle 1 = 30.0°. The bounce reverses the y component of the ball's velocity but does not alter the x component. (a) What is theta_2? (b) What is the change in the ball's linear momentum in unit-vector notation? I got the physics of part b, the trig of part a is messing me up. I went so far as to make a system: [tex]v\cos\theta_2=-v\cos\theta_1[/tex] [tex]v\sin\theta_2=v\sin\theta_1[/tex] As I thought! The angle must be in the second quadrant... so that means add 90 degrees, right? (And not 180-angle?) But I don't know how to go from the typical coordinate system used for measuring angles to the funky one shown in the diagram.