# Linear density

1. Nov 13, 2004

### Alem2000

I had a problem with finding the moment of inertia. I have a rod and it has linear density$$\lambda=4.0kg$$ and the equation for its moment of inertia is $$I=\frac{1}{12} ML^2$$ now I have an axis at the center of mass of a rod the rod has a total length $$L=4m$$ so in my equation I would have to substute $$\lambda L=M$$ now the thing that I dont understand is if my center of mass horizontal cordinate is $$2m$$ the length I multipy by lambda should be 2m correct?

2. Nov 14, 2004

### Sirus

Kg is not the unit for linear density. I'm assuming you meant $4.0\frac{kg}{m}$. If each meter of the rod has a mass of 4.0kg, why would you only multiply by half the length of the rod to get its mass? I think $M=(4.0\frac{kg}{m})(4.0m)$. Does that give you the right answer?