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Two cars colliding example

  1. Dec 1, 2005 #1
    I feel so silly for not being able to work this out.....

    The situation is this - two cars going towards each other. Both cars' mass = 1Kg. The speed of car 1, say, is 5m/s. The speed of car 2, say, is 3 m/s. THE IMPORTANT THING TO NOTE IS THAT BOTH CARS ARE TRAVELLING AT CONSTANT SPEED!

    What i'm trying to work out is what their speed is afterwards!

    I've looked into the impulse = change in momentum equations but the bit that's confusing me is if the cars are travelling at constant speed, then acceleration =0; thus force is 0.... thus impulse = 0?????? which is obviously wrong but i can't prove it.... :(
    Using the impulse method, i assume a contact time of 1 s, for simplicity.

    N.B i'm trying to design a game with realistic motion but i can't do it..... its killing me! Any help will be duly appreciated.
    thanks in advance
    Last edited: Dec 1, 2005
  2. jcsd
  3. Dec 1, 2005 #2
    Hm.... is it something i've not done?
  4. Dec 1, 2005 #3


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    You needn't pull your hair out by using Newton's equations. Instead, apply the conservation of momentum principle. You will also need to assume that they either stick together after the collision or that kinetic energy is conserved to solve.
  5. Dec 1, 2005 #4
  6. Dec 1, 2005 #5


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    Yes. Looks like you're seeing the beauty of physics already =D
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