Homework Help: Banked highway curves and static friction

1. Feb 22, 2009

joseg707

1. The problem statement, all variables and given/known data
A 1200 kg car rounds a curve of radius 67 m banked at an angle of 12 degrees. If the car is traveling at 95 km/hr, will a friction force be required? If so how much and in what direction?

2. Relevant equations
F=ma
a=v2/r

3. The attempt at a solution
I don't know what I'm doing wrong with this problem. These are the two equations I have from them and when I try to solve I either get a huge number or a negative.

Ncos$$\theta$$-Ffrsin$$\theta$$-mg=0

Nsin$$\theta$$+Ffrcos$$\theta$$=ma

I'm positive that it needs friction force and I think it is in the direction of the center of curve, but I haven't figured out a way to solve. Can someone please help?

2. Feb 23, 2009

Delphi51

3. Feb 23, 2009

joseg707

Hey thanks! I think I found out what I was doing wrong. I didn't really take notice that the force of friction was equal to the friction coefficient multiplied by the normal force. Thank you very much!

4. Feb 23, 2009

davieddy

I don't think you did.
Your equations were right but you need to solve for F by eliminating N.

By far the simplest way is to resolve || to the slope in the first place.