Boxes are transported by a conveyor belt with a velocity $\mathbf{v}_{0}$ to a fixed incline at $A$ where they slide and eventually fall off at $\bar{B}$. Knowing that $\mu_{i}=0.40,$ determine the velocity of the conveyor belt if the boxes leave the incline at $B$ with a velocity of $8 \mathrm{ft} / \mathrm{s}$.