Calculating the Moment of Inertia

  • Thread starter erok81
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  • #1
erok81
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Homework Statement



The four masses shown in the attachment are connectec by massless, rigid rods.

a) find the coordinates of the center of mass.
b) find the moment of inertia about a diagonal axis that passes through mass B and D.

Homework Equations



I=MR^2...I think.

The Attempt at a Solution



I've solved part a which ended up being 0.0517m, 0.0517m.

Part b is where I am stumped.

I've tried [tex]I=M_{A}R^{2}_{A}+M_{B}R^{2}_{B}+M_{C}R^{2}_{C}+M_{D}R^{2}_{D}[/tex] using both the radius of the rods as well as the radius of the center of mass, but neither works.

I know I am doing this wrong and it's probably a conceptual thing, but I can't see it. :confused:
 

Attachments

  • Figure One.png
    Figure One.png
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Answers and Replies

  • #2
Filip Larsen
Gold Member
1,570
487
The R's in your equation should be the distance from the rotation axis to the mass in question.
 

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