The moment $\frac{?}{\text{b}\text{a}\text{r}}(M{)}_O$ of the force $\frac{?}{\text{b}\text{a}\text{r}}(F)$ about the point $O($shown in figure below$)$ is defined as

$\frac{?}{\text{b}\text{a}\text{r}}(M{)}_O\frac{?}{b}=ar(r{)}_{\frac{P}{O}}\frac{}{b}ar(F)$ where $\frac{?}{\text{b}\text{a}\text{r}}(r{)}_{\frac{P}{O}}$ is the vector from point $O$ to point $P$ on the line $L.$ This is

typically referred to as the position vector of point $P$ relative to point $O.$ The line $L$ defines the

line of action of the force $\frac{?}{\text{b}\text{a}\text{r}}(F).$ Show that $\frac{?}{\text{b}\text{a}\text{r}}(M{)}_O$ is independent of the location of the point $P$ as long

as point $P$ is on line $L.$