A cone is made from the sector by joining OA to OB. (i) Calculate the radius, r, of the cone. (ii) Calculate the volume of the cone.

From part (a), the arc length $L$ of the sector was calculated as:

$$L = \frac{22}{3}\pi \text{ cm}$$

The circumference of the cone's base is $C = 2\pi r$.

$$2\pi r = \frac{22}{3}\pi$$

Divide both sides by $2\pi$:

$$r = \frac{22}{3}\pi \div (2\pi)$$ $$r = \frac{22}{3} \times \frac{1}{2}$$ $$r = \frac{11}{3}$$ $$r \approx 3.666... \text{ cm}$$

Rounding to two decimal places:

$$r \approx 3.67 \text{ cm}$$

The radius of the cone is $\boxed{3.67 \text{ cm}}$.

The slant height ($l$), radius ($r$), and height ($h$) of a cone form a right-angled triangle, so $l^2 = r^2 + h^2$.
We have $l = 8$ cm and $r = \frac{11}{3}$ cm.

$$8^2 = \left(\frac{11}{3}\right)^2 + h^2$$ $$64 = \frac{121}{9} + h^2$$ $$h^2 = 64 - \frac{121}{9}$$ $$h^2 = \frac{576}{9} - \frac{121}{9}$$ $$h^2 = \frac{455}{9}$$ $$h = \sqrt{\frac{455}{9}}$$ $$h = \frac{\sqrt{455}}{3} \text{ cm}$$ $$h \approx 7.1102 \text{ cm}$$

Using the formula $V = \frac{1}{3}\pi r^2 h$:

$$V = \frac{1}{3}\pi \left(\frac{11}{3}\right)^2 \left(\frac{\sqrt{455}}{3}\right)$$ $$V = \frac{1}{3}\pi \left(\frac{121}{9}\right) \left(\frac{\sqrt{455}}{3}\right)$$ $$V = \frac{121\pi\sqrt{455}}{81}$$ $$V \approx \frac{121 \times 3.14159265 \times 21.3307125}{81}$$ $$V \approx \frac{8100.27}{81}$$ $$V \approx 100.003 \text{ cm}^3$$

Rounding to three significant figures:

$$V \approx 100 \text{ cm}^3$$

The volume of the cone is $\boxed{100 \text{ cm}^3}$.