8. A ship travels uniformly against the current from point A to point B, with the distance between A and B being $s$ (kilometers), the water speed being a constant $p$ (kilometers/hour), and the ship's maximum speed in still water being $q$ (kilometers/hour) $(q>p)$. It is known that the hourly fuel cost (in yuan) is directly proportional to the square of the ship's speed in still water $v$ (kilometers/hour), with the proportionality constant being $k$.
(1) Express the total fuel cost $y$ (yuan) as a function of the speed in still water $\eta$ (kilometers/hour), and specify the domain of this function;
(II) To minimize the total fuel cost, what should the ship's actual forward speed be?
$$
\text { (( I ) } y \leq k s \frac{v^{2}}{v-p}, v \in(p, q] \text {; ( II ) } 2 p \leq q
$$

When $2 p \leq q$, the actual speed of the ship's advance should be $p$. When $2 p > q$, the actual speed of the ship's advance should be $q-p$.