Originally Posted by

**cinder** Physics problem here.

A curve with a $\displaystyle 140 m$ radius on a level road is banked at the correct angle for a speed of $\displaystyle 20 {\rm m/s}$.

If an automobile rounds this curve at $\displaystyle 30 {\rm m/s}$, what is the minimum coefficient of static friction between tires and road needed to prevent skidding?

A friend got me started: $\displaystyle \tan \theta=\frac{20^2}{(9.8)(140)}$, $\displaystyle \theta=16.25$ but I'm not sure why this is important or what to do with it to find $\displaystyle \mu_s$ (friction coefficient).