# Moment of inertia

1. May 19, 2005

### iNCREDiBLE

Hello!

I have a problem and I was kind of hoping that someone could help me out.

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2. May 19, 2005

### whozum

Give us some of your thoughts.

3. May 19, 2005

### iNCREDiBLE

Well I I don't know where to start and what formula to use. As far as I can tell the area is 6x3 = 18 sq ft.

4. May 19, 2005

### HallsofIvy

Staff Emeritus
Okay, here are some hints: What is the DEFINITION of "moment of inertia"? What formulas do you know relating to moment of inertia?

5. May 19, 2005

### jackson

u should actually try and understnd the definition of moment inertia before attempting the question. as u know the I, moment of inertia is affected by the shape of the solid and also at what point it is being referred to, so i had reckon u to understand the definition b4 attempting it.

6. May 19, 2005

### iNCREDiBLE

The understanding tends to come afterwards (for me). The surface = one rectangel + two triangles... For the rectangle I = 4*3^3/12 = 9. The two triangles I = 2(2*3^3/12) = 9. So my answer is 18 ft^4. But is this a correct solution?

7. May 19, 2005

### iNCREDiBLE

Please, can somebody help me & explain it to me...

8. May 19, 2005

### arildno

Could you make a more thourough post on how you got those "answers".
And please, do not use numbers, but symbols.
That makes it easier for us to spot where you've made any mistakes.

9. May 19, 2005

### Pyrrhus

Are you familiar with Steiner's Theorem or Parallel axis Theorem?