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What was the velocity of the Honda

  1. Nov 22, 2010 #1
    In a chain reaction car accident on the North-South tollway, a BMW with a mass of 2000 kg collides elastically with a Honda Civic (mass 1500 kg) at rest. The Honda in turn collides with a Hummer of mass 3000 kg in front of it, that’s also at rest, and the Honda and the Hummer lock bumpers and slide forward with a velocity of 3 m/s. (The BMW that originated the chain of events is not involved in the second collision). What was the velocity of the Honda right after the first collision and before it hits the Hummer?

    My attempt: V=MA/MA+MB

    (2000kg)(0m/s)+(1500)(3m/s)+(3000kg)(3m/s) / 1500kg+3000kg
    Is this correct??
     
  2. jcsd
  3. Nov 22, 2010 #2

    Delphi51

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    Re: collisions

    Can't have this - units of m/s on the left, kg on the last term on the right.
    So, there is an elastic collision and then an inelastic collision, ending up with speed 3. Which collision will you start with? What equation(s) apply to each collision?
     
  4. Nov 22, 2010 #3
    Re: collisions

    You would start with the elastic collision? I don't understand which equation to use
     
  5. Nov 22, 2010 #4

    Delphi51

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    Re: collisions

    I am reluctant to say which end I would start at! Far better for you to see which way to go. I think you will when you write out the equations.

    Do you know what principle applies to all collisions?
    And which one applies only to elastic collisions?
    These should be easy to find in your text book or in
    http://hyperphysics.phy-astr.gsu.edu/hbase/conser.html#cons
    Once you know the conservation law(s) that apply, you will be able to write equations for them. I suggest a diagram with appropriate names for things like the speed and mass of the Honda, etc.
     
  6. Nov 23, 2010 #5
    Re: collisions

    Is it 9.09?
     
  7. Nov 23, 2010 #6

    Delphi51

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    Re: collisions

    I got a number close to that, but not the same.
    Did you start with the last collision? Equation?
     
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