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Homework Help: A Problem Involving Newton's Second Law

  1. Sep 17, 2011 #1
    Once her chute opens, a sky-diver of mass m is acted upon by a downward force Fg due to gravity, and an upward force Fr due to air resistance. If Fg = mg, where g is gravitational acceleration, and Fr is proportional to velocity v, use Newton’s Second Law of Motion to write acceleration a as a function of velocity v.

    Hey guys, I need a help on how to approach this problem. Initially, I assumed Fr = Ff = umg. But the problem states that Fr is proportional to velocity. Help?
  2. jcsd
  3. Sep 17, 2011 #2


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    Newton's 2nd law is
    [tex]\sum_i \mathbf{F}_i = m\mathbf{a}[/tex]What do you get when you apply it to this problem?
  4. Sep 17, 2011 #3
    Proportional meaning, the upward force equals the velocity, times a proportionally constant. Hence the drag force is Fr=bv, where b is a real number and v is velocity.
  5. Sep 17, 2011 #4
    Thanks Xyius! Using your definition of drag force, I was able to work it out!
  6. Sep 17, 2011 #5
    Glad to hear it! :D!
  7. Sep 19, 2011 #6
    Would you care to explain how you did this?
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