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Homework Help: Deceleration question!

  1. Nov 2, 2009 #1
    1. The problem statement, all variables and given/known data

    Leroy, who has a mass of 100kg, is skateboarding at 9.0 m/s when he smacks into a brick wall and comes to a dead stop in .2s

    a. Show that his deceleration is 45 m/s^2.
    b. Show that the force of impact is 4500N.

    2. Relevant equations
    I think the only equations that are needed are these:
    a= NetForce/m
    Weight = mg
    Force= ma

    3. The attempt at a solution

    I tried a number of things, but I couldn't figure out how to get the deceleration. It's not in my book anywhere. All I have are the equations for acceleration. I've tried various configurations, but nothing seems to make sense.
  2. jcsd
  3. Nov 2, 2009 #2
    You can not use only 1 eq to find 2 variables. The 2nd eq you need is:
    v(t) = v0 + at

    Because he stops after 0.2s => v(0.2s) = 0. Plug them and find a => F
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