There are

three forces acting on the car - gravity, a normal force N by the road, and a frictional force by the road. Since the car is accelerating at

(the centripetal acceleration), these must add up to a force

acting horizontally. Since we are looking for the minimum coefficient of friction, set the frictional force to be the maximum possible, given by

where

is the coefficent of friction.

So we have:

(straight down) plus

(perpendicular to the road, up and toward the center) plus

(parallel to the road, up and

away from the center) equals

(horizontal toward the center)

First, calculate

by looking at the components perpendicular to the road:

plus

plus

equals

Then calculate

(and then

) by looking at the components parallel to the road:

plus

plus

equals

You should be able to take it from there. If you're still having trouble, go ahead and post again in this thread.

- Hollywood