The circumference of a circle must be

In the adjoining figure, $O$ is the centre of the circle. If $OA= 5 \mathrm{cm}, AB= 8 \mathrm{cm} \text{and} OD\perp AB$, then length of $CD$ is equal to:

In the given figure, a chord $PQ$ of a circle with centre $O$ and radius $15$cm is bisected at $M$ by a diameter $AB$. If $OM=9$cm, find the lengths of:-

$\left(\mathrm{i}\right) PQ$

$\left(\mathrm{ii}\right) AP$

$\left(\mathrm{iii}\right) BP$