Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Momentum in car collision.

  1. Dec 9, 2009 #1
    When a car of mass 2.0 × 10³ kg moving at 9.0 m/s collides head on with a second car having a mass of 1.5 × 10³ kg, the cars lock and come to rest at the point of collision. (a) What was the momentum of the second car before the collision? (b) What was the velocity of the second car before collision?

    I think this means that F of the first car equals F of the second car. So solve for F of the first car with F = ma. What's the acceleration though? :s Once I get that, equal it to (acceleration of second car)(1.5 × 10³). I can solve for the velocity of the second car somehow I think. Then I could get momentum with p = mv.

    Excuse my ignorance. Physics is not my cup of tea. =(
  2. jcsd
  3. Dec 9, 2009 #2
    u dont need to use F in this problem at all. its all about momentum.
    yes u can solve for the velocity of the second car using conservation of momentum:
    Pi = Pf
    m1v1 + m2v2 = m1fv1f + m2fv2f
    since they come to rest after collision the final momentum is 0.
    so m1v1 = -m2v2

    i think u can solve it from now.
  4. Dec 9, 2009 #3
    m1v1 = m2v2
    (2000 kg)(9.0 m/s) = -(1500 kg)(v2f)
    v2 = -12 m/s

    mv = p
    (1500 kg)(12 m/s) = 1.8 × 10^4 kg×m/s
    Last edited: Dec 9, 2009
  5. Dec 9, 2009 #4
    i wont check it with a calculator, but i see u got the point. :)
  6. Dec 9, 2009 #5
    Thanks. =D
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook