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Force (2)

  1. Sep 22, 2007 #1
    1. The problem statement, all variables and given/known data
    Seat belts and air bags save lives by reducing the forces exerted on the driver and passengers in an automobile collision. Cars are designed with a "crumple zone" in the front of the car. In the even of an impact, the passenger compartment decelerates over a distance of about 1m as the front of the car crumples. An occupant restrained by seat belts and air bags decelerates with the car. By contrast, an unrestrained occupant keeps moving forward with no loss of speed until hitting the dashboard or windshield. These are unyielding surfaces, and the unfortunate occupant then decelerates over a distance of only about 5mm. a.) A 60 kg person is in a head-on collision. The car's speed at impact is 11m/s. Estimate the net force on the person if he or she is wearing a seat belt and if the air bag deploys. b.)Estimate the net force that ultimately stops the person if he or she is not restrained by a seat belt or air bag. c.) How do these forces compare to the person's weight? (They want to know F(a)/W = ? and F(b)/W = ?)


    2. Relevant equations
    F=ma


    3. The attempt at a solution
    I don't even know where to begin with this problem. I sat and read it a couple of times, and just had no idea where to begin.
     
  2. jcsd
  3. Sep 22, 2007 #2

    learningphysics

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    The main part of the problem is to find the acceleration... for the first case initial velocity is 11m/s... he comes to a stop over 1m... what is the accleration?

    second case again initial velocity is 11m/s... he comes to a stop over 5mm... what is the accleeration?

    force is just mass times acceleration.
     
  4. Sep 23, 2007 #3
    Having problems finding the acceleration. I got -60.5.
     
  5. Sep 23, 2007 #4

    learningphysics

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    Yes, that's correct. So what's the force?
     
  6. Sep 23, 2007 #5
    The force would be 3630N? I put that, and it said it was wrong.
     
  7. Sep 23, 2007 #6

    learningphysics

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    Hmmm.... maybe -3630N ? I'm not sure...
     
  8. Sep 23, 2007 #7
    Nope, I tried that too.
     
  9. Sep 23, 2007 #8

    learningphysics

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    I don't understand why it isn't accepting the answer... Is the system sensitive about significant figures?
     
  10. Sep 23, 2007 #9
    I don't think it is. We use WebAssign.
     
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