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1. The problem statement, all variables and given/known data

A 22 kg solid door is 220 cm tall, 92 cm wide.

a) What is the door's moment of inertia for rotation on its hinges?

b) What is the door's moment of inertia for rotation about a vertical axis inside the door, 17 cm from one edge?

2. Relevant equations

[tex]I = \Sigma m_i*r^{2}_i[/tex]

[tex]I_{parallel axis} = I_{cm} + md^{2}[/tex]

3. The attempt at a solution

I was able to get part a by using a given formula for a plane with an axis of rotation around it's edge: [tex]\frac{1}{3}Ma^2 = \frac{1}{3}(22)(.93)^2 = 6.2 kg * m^2[/tex].

For part b, I cannot seem to get the correct answer. I applied the parallel axis theorem, which I understand to be the second equation I listed above. From a given list, I used the equation for a plane with the axis of rotation around it's center: [tex]\frac{1}{12}Ma^2[/tex]. My resulting formula ended up as this: [tex]I_{parallel axis} = (\frac{1}{12}(22)(.92)^2) + ((22)(.17^2))[/tex], which results in [tex]2.2 kg * m^2[/tex], but it was determined to be incorrect.

What am I doing wrong here? Any help would be greatly appreciated.

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# Homework Help: Moment of Inertia for a door

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