Banked Circular Motion with Static Friction

[milky9311]

Q: "If a curve with a radius of 85m is properly banked for a car traveling 65km/h, what must be the coefficient of static friction for a car not to skid when traveling at 95km/h?"

[PLAIN]http://a4.sphotos.ak.fbcdn.net/hphotos-ak-ash4/215513_1974874979462_1470693940_32310002_1293630_n.jpg


2. The attempt at a solution

I found theta

F_Ncos(theta) = mg

(mgsin(theta))/cos(theta) = (mv²)/r

theta = 21.4^o

But next bit i couldn't do.

Wouldnt the centripetal force of the 95km/h car be F_Nsin(theta) + mu_sF_N? as the static friction + the horizontal component of the normal force allows circular motion?

thanks

 

[ashishsinghal]

F_Ncos(theta) = mg

F_Ncos(theta) = mg?? Check that again...