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Jumping out a plane force of wind resistance

  1. Oct 10, 2011 #1
    1. The problem statement, all variables and given/known data

    If you jumped out of a plane you would begin speeding up as you fall downward. eventually due to wind resistance your velocity would become constant with time. after this occurs the magnitude of the force of wind resistance is
    a. slightly smaller than the force of gravity acting on you
    b. equal to the force of gravity
    c. greater than the force of gravity

    2. Relevant equations

    g=v/t

    3. The attempt at a solution
    slightly smaller?????
     
  2. jcsd
  3. Oct 10, 2011 #2

    hotvette

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    Why would that be?
     
  4. Oct 10, 2011 #3
    honestly, im not really sure
    but i think it would be because the only two forces are gravity and air resistance and air restiance would cause it to be slighty smaller
     
  5. Oct 10, 2011 #4

    lightgrav

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    It's true that air resistance would never get "quite" as strong as gravity, so you would continue to gain speed (slightly) till you hit ground.
    BUT
    The question is about AFTER "your velocity becomes constant" .
    IF your velocity is constant, what about those two Forces?
     
  6. Oct 10, 2011 #5
    if your velocity is constant your not accelerating
     
  7. Oct 10, 2011 #6

    lightgrav

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    your acceleration is zero. (we like zero's).
    so the Forces?
     
  8. Oct 10, 2011 #7
    if acceleration is zero the force would be zero?
     
  9. Oct 10, 2011 #8

    lightgrav

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    which is zero?
    gravity? wind resistance? the difference? the sum? the average? ...
     
  10. Oct 10, 2011 #9
    um. you kinda lost me there. gravitys not zero ever? and i wouldnt think wind resistance could be. the average of what?
     
  11. Oct 10, 2011 #10

    lightgrav

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    you said "the force would be zero" ... as if there was only one possible choice.
     
  12. Oct 10, 2011 #11
    well if f=ma and if a=0 then f=0
     
  13. Oct 10, 2011 #12

    lightgrav

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    have you not yet seen Σ ? it is the ΣF = ma
     
  14. Oct 10, 2011 #13
    i have, but i dont remeber what it means
     
  15. Oct 10, 2011 #14
    all forces acting on an object?
    would the answer be equal to gravity?
     
  16. Oct 10, 2011 #15

    lightgrav

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    it means "Sum" ... as in "it is the Sum of Forces that cause a mass to accelerate".

    You add the constant gravity Force vector (which direction?)
    to the increasing air resistance Force vector (which direction?)
    to get the mass to accelerate with a getting smaller and smaller (downward) till zero.
     
  17. Oct 10, 2011 #16
    gravity vector is down air resistance is up.
    so the answer is b?
     
  18. Oct 10, 2011 #17

    lightgrav

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    yes. (after you've achieved "approximately constant velocity" = terminal speed)
     
  19. Oct 10, 2011 #18
    sweet thanks
     
  20. Oct 10, 2011 #19

    lightgrav

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    yes (after reaching "terminal speed" = approximate constant velocity)
     
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