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Finding ratio of smaller terminal velocity to larger terminal velocity

  1. Feb 12, 2013 #1
    The terminal speed of a sky diver is 188 km/h in the spread-eagle position and 320 km/h in the nosedive position. Assuming that the diver's drag coefficient C does not change from one position to the other, find the ratio of the effective cross-sectional area A in the slower position to that in the faster position.


    vt = sqroot (2mg/pAC)


    188=sqroot(2(90)(9.8)/(1)(A)(1))

    320=sqroot(2(90)(9.8)/(1)(A)(1))

    Basically I just set v to each value given, set everything else the same and solved for A then divided the smaller value by the larger one and got .34 but this was the wrong answer.

    Really thought this was a pretty simple thing to figure out but I'm probably just making a stupid mistake? Thank you!
     
  2. jcsd
  3. Feb 12, 2013 #2
    Re: Finding ratio of smaller terminal velocity to larger terminal velo

    "find the ratio of the effective cross-sectional area A in the slower position to that in the faster position."

    Should the ratio be greater than or less than unity?
     
  4. Feb 12, 2013 #3
    Re: Finding ratio of smaller terminal velocity to larger terminal velo

    I'm sorry, what do you mean by unity?
     
  5. Feb 12, 2013 #4
    Re: Finding ratio of smaller terminal velocity to larger terminal velo

    Unity means the number one. Should the ratio be greater than or less than one?
     
  6. Feb 12, 2013 #5
    Re: Finding ratio of smaller terminal velocity to larger terminal velo

    Ok yeah I see it should be greater than 1 since the area of A for the slower one would be greater than for the faster one...but was it still ok to approach the problem the way I did?
     
  7. Feb 12, 2013 #6
    Re: Finding ratio of smaller terminal velocity to larger terminal velo

    Ok it was just the reciprocal! Thank you very much :)
     
  8. Feb 13, 2013 #7
    Re: Finding ratio of smaller terminal velocity to larger terminal velo

    Glad you got it. I was trying to give you a subtle hint rather than saying take the reciprocal.
     
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