Hi Please see image link for the question (because there is a diagram) I have no idea to where even start with this! All help appreciated, thanks
Hints: $r(0) = b$. Figure out the radius of the circle of rotation, and use that to determine a parametric formula for $r$ in terms of $\cos t$ and $\sin t$ ($t$ is time). Note that $\omega$ is a constant vector in the same direction as $a$.