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tbarker5
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Homework Statement
In the figure F1= 27.9KN, F2= 39.8KN, F3= 61.8KN
What distance d is required for the net couple moment on the triangle to be 1140 counterclockwise?
Express your answer to three significant figures and include the appropriate units.
link to image http://imgur.com/cBnLJ
Homework Equations
I'm thinking the only really relevant equation is Mc=rXf or Mc=|r||F|sin(theta)
The Attempt at a Solution
So I wrote each moment in terms of d using trig. I got:
Mf1= 27900d Nm
Mf2= 19900d Nm
Mf3= 61800cos(30)d Nm
Then I set the sum of the three moments (with direction taken into respect) equal to 1140 Nm.
1140 = 11900d + 61800cos(30)d - 27900d
d~= 0.03038 m or 3.04*10^-2 m.
Unfortunately this was wrong and I have no clue where I went wrong. Any help would be greatly appreciated.