The velocity (in centimeters per second) of blood $r \mathrm{cm}$ from the central axis of an artery is given by
$$v(r)=k\left(R^{2}-r^{2}\right)$$
where $k$ is a constant and $R$ is the radius of the artery (see the accompanying figure). Suppose $k=1000$ and $R=0.2 \mathrm{cm} .$ Find $v(0.1)$ and $v^{\prime}(0.1),$ and interpret your results.