What's wrong with my solution? -- Area moment of inertia

AI Thread Summary
The discussion centers on the application of the parallel axis theorem to calculate the area moment of inertia, with the original poster struggling to find an error in their solution. They discovered that the theorem can determine the moment of inertia about any axis using the moment about a parallel axis through the center of gravity. Key advice includes ensuring that only three moments of inertia need to be added, with the parallel axis theorem applied to specific areas while not needed for others. Additionally, verifying the accuracy of input numbers is crucial, and using a spreadsheet for calculations is recommended for better accuracy. The conversation emphasizes the importance of correctly applying the theorem and checking calculations to resolve the issue.
mobsaleh
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Homework Statement
Area moment of inertia is to be calculated for a composite shape
Relevant Equations
For rectangle: Ix = bh^3/3. For a semi-circle Ix = pi/8*a^4
I used the parallel axis theorem to solve the question but my answer is still wrong. Any ideas where I slipped? I can't seem to figure out the problem?
 
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It seems to me that you only need to add three moments of inertia; no need to subtract anything. You have expressions for all the colored shapes that make up the object. For the green and red areas you need to use the parallel axis theorem but not for the blue area. Other than that, you need to make sure that all the input numbers are correct. I would use a spreadsheet instead of a calculator for this.
Inertia.png
 
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