A projectile is launched over horizontal ground at an angle between $0^{\circ}$ and $90^{\circ}$.
a. Is there any point on the trajectory where $\vec{v}$ and $\vec{a}$ are parallel to each other? If so, where?
b. Is there any point where $\vec{v}$ and $\vec{a}$ are perpendicular to each other? If so, where?