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Homework Help: Terminal velocity

  1. Feb 13, 2008 #1
    v^2= (4mg)/A

    so if a 22cm diameter ball has a terminal velocity of 85m/s, what would the mass of the ball be?
    A = 4pi r^2
    22cm= 0.22m
    v^2 = (39.2m)/(4pi (.11)^2)
    7225= (39.2m)/(pi*.0484)
    So I got 28kg for the mass and that is not right. Please help.

    Stephen Doty
  2. jcsd
  3. Feb 13, 2008 #2


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    You have incorrectly noted that A=4pi r^2, where of course you meant A= pi r^2.
  4. Feb 13, 2008 #3
    I know the area of a circle is pi r^2
    but isnt the area of a sphere or a ball 4pi r^2 ????
  5. Feb 13, 2008 #4
    In problems with air resistance we use area of the largest cross section of an object with a plane that is perpendicular to its direction of movement. In this case that is a circle with radius r
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