This is a repost because i realized i put it on the wrong forum section. After getting Kleppner and Kolenkow's second edition textbook I began my exploration of physics. I'm a sophomore in high school and VERY ignorant in regards to physics so if this question make no sense set me straight. I would appreciate it you told me what mistakes I made throughout the problem and how you would solve it. I devised the following problem for myself: Asteroid 1 with a Mass of 300 Kg and a Velocity of V = (20i + 4j - 12z) collides with Asteroid 2 with a Mass of 1800 Kg and a Velocity of V = (-3i - 16j -32z). What is the Angle between the two Asteroids after the collision? What are the two Asteroid's velocities after the collision? 1. I found the Momenta of the two asteroids. (P1 is Asteroid one's momentum. P2 is Asteroid two's momentum.) Because mass is a scalar quantity, I multiplied the Components of velocity by Mass. P1 = 300(20i + 4j - 12z) = (6000i + 1200j - 12k) P2 = 1800(-3i - 16j - 32z) = (-5400i - 28800j - 57600k) 2. Then I got the Angle between the two Momenta Vectors. cos (θ) = (P1 ⋅ P2) / |P1||P2| = 72.18° My problem is that i dont know how to obtain the Asteroid's momentum or Velocity after the collision.