Calculating Normal Force Acting on Car at Point B

[BuBbLeS01]

Homework Statement

A car with a mass of 1190 kg is traveling in a mountainous area with a constant speed of 78.2 km/h. The road is horizontal and flat at point A, horizontal and curved at points B and C. The radii of curvatures at B and C are: rB = 155 m and rC = 120 m.

Calculate the normal force exerted by the road on the car at point B.

Homework Equations

Forces...
x = f = mv^2/r
y = -mg + n = 0

The Attempt at a Solution

If n = mg then where does the radius come into play? I must have something set up wrong in the forces but I don't know what.

 

[learningphysics]

I think the curves are supposed to be the tops of hills right?

So N - mg = mv^2/r (during a valley because the center of curvature is towards the top)

mg - N = mv^2/r (during a hill because the center of curvature is towards the bottom)