# Homework Help: Finding the coefficient of static friction

1. Mar 11, 2010

### dapperjon002

1. The problem statement, all variables and given/known data
If a curve with a radius of 85m is properly banked for a car traveling 65 km/h what must the coefficiant of static friction be for a car not to skid when traveling at 95km/h

2. Relevant equations
For this question i tried using a few equations such as centripical force, force friction where Ffric = UsFn aswell as (mv^2)/R = Ffric i also though the equation Tan(theta)=V^2D/Rg was pertanent.

3. The attempt at a solution
I set up a proportion of mv^2/R = Us(ma) and the masses canceled out so i was left with v^2/ra but i didnt really know where to go from here.

2. Mar 11, 2010

### benhou

Welcome to Physics Forum, although I am quite new too.
The car is moving on a banked curve. Did you take in account the part of the normal force that points towards the centre $$N_{x}$$? Also, you should also break the friction force into components $$f_{x}$$ and $$f_{y}$$.

3. Mar 11, 2010

### dapperjon002

Ok i set up my two force components and i have Fycos(theta)=mg and Fxsin(theta)=mv^2/r when dividing both components together you are left with tan(theta)=v^2/rg and when i plug in the numbers given after converting 95 km/h to m/s you get a static friction of .81 am i doing somthing wrong because it doesn't seem right

4. Mar 11, 2010

### benhou

What did you mean by Fy and Fx?

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