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Terminal Velocity and Resistive Forces problem

  1. Nov 16, 2008 #1
    1. The problem statement, all variables and given/known data
    A sky diver of mass 81.5 kg jumps from a slow-moving aircraft and reaches a terminal speed of 50.0 m/s.
    (a) What is the acceleration of the sky diver when her speed is 30.0 m/s?

    2. Relevant equations
    mg = bv
    where b is the friction constant
    and v is the terminal velocity

    3. The attempt at a solution
    b = (81.5)(9.8) / 50
    b = 15.97

    (81.5)(9.8) - (15.97)(30) = remaining force, or 319.6 Newtons
    319.6 N / 81.5 = 3.921

    but it seems, 3.921 is not correct. I must be missing something big.
    Any help would be appreciated.
    Last edited: Nov 16, 2008
  2. jcsd
  3. Nov 16, 2008 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    A number of things could cause your answer to be off.

    Firstly, if you are entering your answers online be careful with your significant figures - online marking software can be very pedantic about such things.

    Secondly, were you explicitly told that the drag force was a linear function of velocity because for large objects moving faster than a few m/s the drag force is usually a quadratic function of velocity.
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