# Moment of inertia, double integral

1. Apr 14, 2014

### Feodalherren

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

2. Relevant equations

3. The attempt at a solution
For part B, why is he using the formula for the moment of inertia about the y-axis? Why isn't he using the formula for the moment of inertia about the origin?

http://www.math24.net/physical-applications-of-double-integrals.html

The formula that I'm referring to is the "polar moment of inertia" in this list.

2. Apr 14, 2014

### maajdl

We can't read any problem statement and relevant equations in you post.
What's the question?

Note that a moment of inertia is always defined with respect to an axis (of rotation).
There is nothing like a moment of inertia about a point like the origin.

3. Apr 14, 2014

### Feodalherren

You can't see the picture? I can see it :/.

The formulas are in the link.
I don't know what to tell you. The problem is asking for moment of inertia about the origin. The list of integrals also has a formula for "polar moment of inertia".