two identical billiard balls are on a frictionless, horizontal surface. ball 1 has an initial velocity of 5.00 m/s in the positive x direction, and ball 2 is initially at rest. the balls collide, and, after the collision, ball 1 is moving at a speed of 2.00 m/s at an angle of theta = 30.0 below the positive x axis, as shown in the diagram