In an experiment to measure the speed of light using the apparatus of Armand H. L. Fizeau (see Fig. 34.2 ), the distance between light source and mirror was $11.45 \mathrm{~km}$ and the wheel had 720 notches. The experimentally determined value of $c$ was $2.998 \times 10^{8} \mathrm{~m} / \mathrm{s}$ when the outgoing light passed through one notch and then returned through the next notch. Calculate the minimum angular speed of the wheel for this experiment.