# Moment of Inertia

1. Nov 7, 2008

### uno

1. Determine the moment-of-inertia in kg/m^2 of a solid disk 0.51 m in diameter, having a mass of 5.0 kg.

2. I=mr^2

3. I thought the formula was I = mr^2. Mass = 5kg and the radius = .255m, but when I enter the answer of .325 it is incorrect. Am I using the correct formula? Thanks.

2. Nov 7, 2008

### Dick

No. mr^2 is correct for a cylindrical shell. Your disk is solid. Why don't you look up the correct formula?

3. Nov 7, 2008

### uno

You know what DICK? I am studying physics for the 1st time and I am working very hard at it so I would appreciate a little courtesy for those of us who "aren't as smart as you"

4. Nov 7, 2008

### Dick

Apologies for being direct, but look. If you think you might have the wrong formula, you might try to look up the formula for the MOMENT OF INERTIA OF A DISK. Is that too much to ask? Geez. Aren't you being a little quick to take offense? Do you expect me to just tell you the answer? Then you are asking too much.

5. Nov 8, 2008

### uno

I apologize for jumping to offense. I just get frustrated with all of this and it takes me a while to understand some of the problems.

Thanks for helping out.

6. Nov 8, 2008

### Dick

That's ok. I understand people get stressed with unfamiliar material and sometimes I see the answer as far more obvious than they do. You did get it right?

7. Nov 8, 2008

### uno

Yes, I got it. Thanks again.