A banked circular road is designed for traffic moving at 60 km/h. The radius of the curve is 200m. On a rainy day (I think this means to assume there is no friction in determining the bank angle) traffic moves at 40km/h. What is the minimum coefficient of friction between the tires and the road that will allow cars to negotiate the turn without sliding off the road?
I use the formula to get the bank angle of the road, assuming theres no friction on the rainy day. I don't know what to do from here, though, to find the coefficient of static friction between tires and the road.