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Homework Help: Settting up force problem with only mass and velocity provided

  1. Oct 19, 2011 #1
    1. The problem statement, all variables and given/known data

    A 60kg person is in a head-on collision. The car's speed at impact is 15 m/s. Estimate the net force on the person if they are wearing their seat belt and the air bags deploy. When these two events occur, the passenger decelerates over a distance of 1 m.

    2. Relevant equations

    This is a force problem so I reasoned I would need to use F=ma. Below explains other equations I try.

    3. The attempt at a solution

    This is the way I saw it. I need "F" and I have "m", but they gave me a velocity instead of an acceleration. Although I need an acceleration, I don't know how to set up the kinematics problem (I greatly struggle with this part of each problem) and I try all different things that don't make sense. So I have V_f = 0 m/s while V_i = 15 m/s but all the equations I tried still have an unknown "time" or "distance", which I don't understand how to extrapolate out of the problem. Would I use D_i as 1 m and D_f as 0 m since it decelerates over a distance of 1 m?
     
  2. jcsd
  3. Oct 19, 2011 #2
    You are first looking for your acceleration, so you are going to ignore the F=ma until you know "a"

    https://www.physicsforums.com/showthread.php?t=110015
    find the equation that had distance, acceleration, and a starting velocity, and a final velocity

    vf^2=vi^2+2aΔx
     
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