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

[mobsaleh]

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?

 

[mobsaleh]

Sorry I'm new here. I didn't know how to attach earlier in my original question

 

[mobsaleh]

NVM, I found my answer in Wikipedia: The parallel axis theorem can be used to determine the moment of inertia or the second moment of area of a rigid body about any axis, given the body's moment of inertia about a parallel axis through the object's center of gravity and the perpendicular distance between the axes.

 

[Lnewqban]

Also here:
http://hyperphysics.phy-astr.gsu.edu/hbase/parax.html

http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html#mi

:)

 

[kuruman]

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.