Inertia of System: Find w/ Pink Dot & Diagonals

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SUMMARY

The inertia of a system with respect to a rotation axis through the center of mass (the pink dot) is calculated as 4(mr²). The discussion clarifies that the radius (r) is defined as the perpendicular distance from the mass to the axis of rotation, which is 3 (derived from 6 divided by 2), rather than sqrt(13), which incorrectly represents the distance from the mass to the center point. This distinction is crucial for accurate calculations of inertia in rotational dynamics.

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Hanin
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Hi, in the following problem, I need to find the inertia of the system. The axis of rotation passes through the center of mass ( the pink dot). I understand that I will be equal to 4(mr^2). However, I do not understand why r= 3 (6 divided by 2) and not sqrt13 ( half of the diagonal of the rectangle).

upload_2017-12-8_20-27-53.png

 

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Review your definitions. r is the perpendicular distance from the mass to the axis of rotation, which is that entire line through the center, not the distance from the mass to the point in the center.
 
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I think you were thinking rotation about the c.g. into/out of page.
 

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