I'm just wondering: in the case when there is 3 balls and ball 2 and ball 3 is stationary. Ball 1 hits ball 2 then stops and ball 2 hits ball 3. Ball 2 moves at an angle of let's say 30 degrees to the left and ball 3 moves at an angles of 60 degrees to the right. You then combine the vectors to form a right triangle. The hypotenuse is the momentum of the 3 balls initially. Would the hypotenuse just be the momentum of ball 1since the rest are stationary?