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Finding initial speed of 'Porsche' using inelastic collision with reference frame

  1. Oct 7, 2009 #1
    1. The problem statement, all variables and given/known data
    blah blah blah
    2. Relevant equations
    momentum = momentum'
    mv + mv = (m1+m2)v
    (Uk)N = friction force


    3. The attempt at a solution

    It's hard to find how to start with randomly given values.
    Thank you so much for your help! :D
     
    Last edited: Oct 7, 2009
  2. jcsd
  3. Oct 7, 2009 #2

    Delphi51

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    Homework Helper

    It is a 2D problem so you must write two headings for North/South and East/West. Then write that "momentum before = momentum after". Follow that up with an "mv" for each moving object in each part. Then put in your numbers. If you are still having trouble, show us your work and someone will be pleased to pitch in and help!
     
  4. Oct 7, 2009 #3

    Delphi51

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    Homework Helper

    No, I don't think any of it makes sense. Even the
    1380kg v + 2304kg v = 3684kg v
    can't be right because before the collision you don't have two vehicles moving in either the north/south or east/west direction. Got to write the two headings and two separate equations!

    You do have to find the speed of the pair of them after the collision from the friction and distance information given. That is an ordinary 1D accelerated motion problem, a little complicated because there is no time info. Do you have the accelerated motion formula with v's, d and a but no t? That is perfect for the job. If you don't have it you could derive it by solving Vf = Vi + at for t and subbing into
    d = Vi*t+.5*a*t^2. Or you could sketch the v vs t graph and use the fact that the area under the graph is the distance.
     
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