Answer
$V(r)=\dfrac{2}{3} \pi r^3$
Work Step by Step
We know that the height is twice the radius, so $h=2r$
The volume is given as:
$V=\dfrac{1}{3} \pi r^2 h$
Therefore, the composite function is:
$V(r)=\dfrac{1}{3} \pi r^2 h=\dfrac{1}{3} \pi (r^2) (2r)=\dfrac{2}{3} \pi r^3$
