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Homework Help: What is the average force?

  1. Nov 20, 2008 #1
    1. The problem statement, all variables and given/known data
    A 1200 kg car drives headlong into a brick wall at 14 m/s and rebound at 3 m/s. The collision lasts for .10 seconds. What is the average force on the car during the collision?

    2. Relevant equations
    f*change in time= mass * change in velocity
    f= mass*change in velocity / change in time

    3. The attempt at a solution
    I got the change in velocity to be 17 m/s. I did 14 m/s - (-3m/s) = 17 (I put the 3 as negative since it it rebounding it is going in the negative x direction.
    f= 1200(17)/ .1 = 204,000. this is wrong..where am I messing up?
  2. jcsd
  3. Nov 20, 2008 #2


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    Science Advisor
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    Gold Member

    The change in velocity is (final v - initial v). You may have a signage error. And don't forget the force unit.
  4. Nov 20, 2008 #3
    Looks good to me, except for you not including the correct unit for force.
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