Question

Two cars collide with each other. Before the collision, one car (m = 1300 kg) is going north at 30 m/s and the other car (m = 900 kg) is going south at 15 m/s. What is the momentum of the system made up of the two cars after the collision?

Answer 1

momentumis defined as\[p=mv\]now draw it out. always draw it out first when it's questions like this. i feel like it helps a lot if you understand what's going on in the question. less thinking about what's going on and more time thinking about what you can solve. hmmm... your question doesn't indicate that the cars go in their separate directions so i'm going to assume that the collision is an in-elastic collision so we get\[m_1v_1+m_2v_2=(m_1+m_2)v_f\]you're looking for the momentum after the collision so that's the stuff on the right side of the equal sign but you don't know the final velocity so you'll need both sides. so to do that you'll put in what you know to both sides. and solve for vf. but since momentum is conserved here i think that means that the momentum before the equation should be equal to the momentum after the equation. i could be wrong because i just got a C in my physics class but i did do well in momentum. :P

Answer 2

also remember that velocity has direction so you need to designate which direction is the positive direction. i usually just go with up as positive and down as negative. now with coordinate system, if you are traveling South (down) that should be negative. so you velocity value for anything traveling South should be negative and the velocities of anything traveling North should be positive.