The following problems consider launching a cannonball out of a cannon. The
cannonball is shot out of the cannon with an angle \(\theta\) and initial
velocity \(\mathbf{v}_{0}\). The only force acting on the cannonball is gravity,
so we begin with a constant acceleration \(\mathbf{a}(t)=-g \mathbf{j}\).
Find the position vector \(\mathbf{r}(t)\) and the parametric representation for
the position.
