angular and linear velocity problems

[amy]

Need help with following problem:
A tack travels 15cm on the rim of a tire while the spoke of the tire travels through 2/3 pi radians. What is the radius of the tire?

Not even sure which formula to use. Would it be s=ro

 

[skeeter]

\(\displaystyle \L s = r\theta\)

\(\displaystyle \L \frac{s}{\theta} = r\)

\(\displaystyle \L \frac{15}{\frac{2\pi}{3}} = r\)

\(\displaystyle \L \frac{45}{2\pi} = r\)