Physics - Rotation Question with Solution | TestHub

Key Idea Torque is an axial yector ie, its direction is always perpendicular to the plane containing vectors $\overrightarrow{\mathrm{r}}$ and $\overrightarrow{\mathrm{F}}$. $$\vec{\tau }=\overrightarrow{\mathrm{r}}\times \overrightarrow{\mathrm{F}}$$ Torque is perpendicular to both $\vec{r}$ and $\vec{F}$ $$\therefore \begin{array}{rl}\vec{\tau }\cdot \overrightarrow{\mathrm{r}}& =0\\ \overrightarrow{\mathrm{F}}\cdot \vec{\tau }& =0\end{array}$$