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Newton Law Question help

  1. Jul 29, 2012 #1
    1. The problem statement, all variables and given/known data
    http://postimage.org/image/810vdcuvf/ [Broken]


    2. Relevant equations

    F=ma

    3. The attempt at a solution

    for part a) i put mdv/dt = -F(brake) - kv

    but is lost for what to put in for part b), help?
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jul 29, 2012 #2

    Doc Al

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    Staff: Mentor

    What is v at t = 0?
     
  4. Jul 29, 2012 #3
    for part b) am i right if i say that

    -the speed is 15 when t=0
    -the speed is decreasing
     
  5. Jul 29, 2012 #4

    Doc Al

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    Staff: Mentor

    The first is what I would call the initial condition.
     
  6. Jul 29, 2012 #5
    c) 1200 dv/dt = -(3600 + kv)
    1/(3600+kv) dv = -1/1200 dt

    so do i integrate the above equation to find k?
     
  7. Jul 29, 2012 #6

    Doc Al

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    Staff: Mentor

    You're not finding k (I assume that k is given in your model of air resistance), but v(t).
     
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