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Math Help - Help on a simple circle formula

  1. #1
    Newbie
    Joined
    Feb 2008
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    16

    Help on a simple circle formula

    Hey guys, I'm stuck on how to find . How did they get it/what is it?

    Question:





    Answer:
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  2. #2
    Junior Member
    Joined
    Dec 2009
    Posts
    38
    This is how I would work out the volume

    A = surface area
    t = thickness (0.01m)
    a = angle between vertical and radius line
    R = Radius of circle ( 60m)
    r = horizontal radius = Rsina
    s = distance along surface in meriden direction

    circufrence of a ring circle = 2*pie*r = 2*pie*Rsina

    Surface area is the just the sum of all the horintal circufrences ie

    \int{2*pie*Rsina ds} (with limits s and 0)

    However easier to transform into angles to work out

    ds = Rda (using angle*Radius = chord length)
    0 = 0
    s = pie/6

    \int{2*pie*Rsina Rda} (with limits pie/6 and 0)

    Area = 2*pie*R^2* ( 1- sqrt(3)/2)

    Mass = density*A*t

    Work it out and see if its right?
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