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posted by  AJam on 10/31/2009 3:35:55 PM  |  status: Closed  |  Earned Karma: 35

moment of inertia

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Classical Mechanics N/A N/A N/A 11/2/2009 at 8:00:00 PM
Question Details:
                                          since this is symetric across the y axis does x bar =0 need help solving for y
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posted by Sapere Aude on 10/31/2009 8:25:22 PM  |  status: Live
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Response Details:
exactly!!!
x bar is zero, and ybar is 11.2
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posted by AJam on 11/2/2009 8:29:03 AM  |  status: Live
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Response Details:
how did you get 11.2 I got ybar=2.5
ybar=(ybar1*Area1-ybar2 *area2+ybar3*area3)/Area Total
c1(0,2.5)A1=2420
c2(0,2.5) A2=-1980
c3(0,2.5) A3=270
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posted by Root_Locus(MNK) on 11/2/2009 9:53:51 AM  |  status: Live
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Response Details:
Beacuse of symmetry x(bar) = 0
for calculation of y(bar) let the above area is combination of two areas,


A1 = 44*10 = 440 mm2
A2 = (20+25)*6 = 270 mm2
x coordinate centroid of area A1 = 0
y coordinate centroid of area A2 = 20 + (10/2) = 25 mm
x coordinate centroid of area A2 = 0
y coordinate centroid of area A2 = -{(20+25)/2 - 20} = -2.5 mm
∴y(bar) = (A1y1 + A2y2)/(A1+A2)
            = (440*25 + 270*-2.5)/(440+270)
            = (11000 - 675)/710
            = 14.54 mm
from here also we can see that
x(bar) = (A1x1+A2x2)/(A1+A2)
          = 0
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