# Homework Help: Parallel Axis Theorem

1. May 9, 2010

### mayaitagaki

Hi everyone,
I've got stuck on this prove problem

Let S be a rectangular sheet with sides a and b and uniform density, and total
mass M.

(a) Show that the moment of inertia of S about an axis L that is perpendicular to S,
meeting S through its center, is

I =1/12*M(a^2 + b^2)

(b) Use the Parallel Axis Theorem in combination with part (a) to show that the moment of inertia of S about an axis L' that is perpendicular to S, meeting S through one of its corner, is

I =1/3*M(a^2 + b^2)

Theorem and an example!

Thank you,
Maya

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2. May 9, 2010

### vela

Staff Emeritus
You need to show some work first so we can see where you're getting stuck.

3. May 9, 2010

### mayaitagaki

I think I kind of got the part a. Then, I don't know how to go from there....

Thank you,

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4. May 9, 2010

### vela

Staff Emeritus
In the parallel-axis theorem, h is the distance from the center of mass of the object to the new axis. In your case, it would be the distance from the center of the slab to the corner. What is that in terms of a and b?