Is My Calculation of Moment of Inertia Using the Parallel Axis Theorem Correct?

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Homework Help Overview

The discussion revolves around the calculation of the moment of inertia (MoI) using the parallel axis theorem. Participants are examining the correctness of an approach taken by the original poster in their attempt to solve the problem.

Discussion Character

  • Exploratory, Assumption checking, Mixed

Approaches and Questions Raised

  • Participants discuss the original poster's method and the use of variables in the expression for MoI. Some suggest alternative approaches, such as using the parallel axis theorem in a different manner.

Discussion Status

There are multiple interpretations of the problem being explored, with some participants affirming the original poster's approach while others suggest different methods. Guidance has been offered regarding the use of variables and alternative calculations.

Contextual Notes

Some participants question the assumptions made regarding the mass distribution and the setup of the problem, indicating that further clarification may be needed.

Romain Nzebele
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Homework Statement
If M=0.50Kg, L=1.2 m, and the mass of each connecting rod shown is negligible, what is the moment of inertia about an axis perpendicular to the paper through the center of mass? Treat the mass as particles.
Relevant Equations
Xcm=total mx/ total m
The picture of the problem and my attempt to solve it are below. Please let me know if my resolution is correct. Thank you in advance.
242976
1557069337351.png
 
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Yes, it looks right. Personally, I would have kept ##M## and ##L## until you had a single expression for the MoI. In this case ##3.2ML^2##.
 
PeroK said:
Yes, it looks right. Personally, I would have kept ##M## and ##L## until you had a single expression for the MoI. In this case ##3.2ML^2##.
Great, thank you so very much.
 
A slightly easier way is to use the parallel axis theorem 'in reverse'.
Find the MoI about the central mass M and subtract (Σm)x2, where x is the displacement to the common mass centre.
 

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