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Homework Help: Car collision, force exertion and impulse.

  1. Jun 13, 2009 #1
    Hello everyone, I have a question which I have no idea how to work out.

    Question: During a collision between two cars, a passangers head strikes an unpadded dashboard with an average force of 48N. This force is exerted for 3x10-3s. If suitable padding had been present the impact would have lasted for 0.6s. Explain with calculations how this would reduce injuries in collisions.

    The only equation I know that involves force is F=mXa, but I don't think that's even relevant to this question.

    I don't know how to attempt this question as my teacher never gave us a question like this before. If you could give me some feedback that would be awesome.
  2. jcsd
  3. Jun 14, 2009 #2


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    Well, here's the situation: the passenger's head is moving at some particular velocity. Then it collides with the dashboard, which slows it down to zero velocity. That much is always true, no matter how much padding is present on the dashboard. The effect of the padding is to spread out that slowdown over a longer period of time. Think about this: what effect does that have on the average force?
  4. Jun 14, 2009 #3
    Sorry about not understanding but I still don't get how to calculate it all out. I know that the 0.6s is better as there is more time for the force to spread out as the head hits the dashboard. But I just don't know how to use calculations for this question.
  5. Jun 14, 2009 #4


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    You have the correct formula. Can you explain to me what the a stands for? Explain it in terms of speed then try to link it to your question.
  6. Jun 14, 2009 #5
    Two more formulas you should find helpful here are:
    J = F*dt = dP
    Where F is the average force. Keep in mind that in both collisions, the impulse the head will be providing to the dashboard will be the same.
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