## Physics: Principles with Applications (7th Edition)

a. Using the hint, find the area between the concentric circles, and set it equal to the length multiplied by width of the path. Let R1 and R2 be the small and large radii. $$\pi R2^{2} - \pi R1^{2} = lw$$ $$l = \frac{\pi R2^{2} - \pi R1^{2}}{w} = 5.4 \times 10^{3} m$$ b. $t = \frac{l}{1.2 m/s} = 4500 s$.