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Car collision problem

  1. Feb 26, 2009 #1
    1. The problem statement, all variables and given/known data
    A 1,000 kg car traveling East at 20 m/sec collides with a 2000kg car traveling East at 5m/sec. They stcik together on impact.
    Find - P(initial)
    Find-Final Velocity
    Find- Change in KE

    2. Relevant equations

    3. The attempt at a solution

    I have no idea how to do this, can someone help me and show the formulas as well so I can learn it? Thanks
  2. jcsd
  3. Feb 26, 2009 #2


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    Homework Helper

    Start with
    momentum before = momentum after

    Write an mv for each moving object, before and after.
  4. Feb 26, 2009 #3
    Do you know how to solve the problem? It would help a lot if I saw it done. I am pressed for time and have 3 exams tomorrow and this is one question i was not sure of for my physics exam.
  5. Feb 26, 2009 #4


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    Homework Helper

    It would not make sense for me to just do your homework for you.
    There must be examples of a collision problem in your notes, your text book and of course on the web. Or we can just plug along with it here, with you doing some of the work.

    Start with
    momentum before = momentum after
    mv + mv = mv
    Put in some numbers?
  6. Feb 27, 2009 #5
    I dont think it was very nice that you wouldnt actually solve the problem for me. The professor did not teach it, there are no similar problems or formulas in the textbook and its not hw. The test was today and I had to pretty much leave that one unfinished. Anyway I would still like to learn it. Oh yea and I searched the web for about 45min and couldnt find anything.

    1000kgx20m/s + 2000kgx5m/s = 20000kg/m/s + 10000kg/m/s= 30,000
    Is that correct so far?
    What would the units be for the outcome?
    What next?
  7. Feb 27, 2009 #6
    Dont start moaning that people wont do you work for you. We're here to help not spoon feed you.

    1. Why did you learn this so late.
    2. Why was it on the test if you've not learnt it and
    3. If its not homework, why post it in the homework section.

    Now onwards.
    You are ok so far. You want to find the final velocity.

    mv (car1)+mv (car2) = mv of crash.

    So: you know know the mv after the crash and the mass of the object (sum of mass of cars). Then you can find v.

    Use this to then find k.e.
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