posted by bob .
Friction provides the force needed for a car to travel around a flat, circular race track. What is the maximum speed at which a car can safely travel if the radius of the track is 82.0 m and the coefficient of friction is 0.39?
You must be refering to the coefficient of STATIC friction, Us, which determines the force at which slipping begins.
Solve this equation for Vmax:
M*Vmax^2/R = M*g*Us
Note that the mass M cancels out.
Vmax = sqrt(g*Us*R)