I am trying to find the moment about a neutral axis I know h

I am trying to find the moment about a neutral axis. I know how to find a moment about a point- but how do you take a moment about a whole axis?

Solution

In order to find moment about an axis, first we need to find moment about a point on the axis and then take the dot product of the moment and unit vector of the axis.

Let r_p be the unit vector of an axis p, and M_o be the moment about a point O on the axis. The moment M_p of force F about the axis p can be expressed as dot product

M_p = r_p.M_o