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## Homework Statement

If a curve with a radius of 88m is perfectly banked for a car traveling 75km/hr, what must be the coefficient of static friction for a car not to skid when traveling at 95km/hr?

## Homework Equations

i guess relevant equations would be tan θ = v^2/rg, but its says next to friction not needed?

f=ma or fr=mar

and Ffr = µs x Fn

## The Attempt at a Solution

I made a free body diagram and since it said it was banked i set that in the y axis theres no acceleration, so following the book (Giancoli), I got Fn=mg/cos θ. I solved for that and got 95^2/(88)(9.8) = .40 then inverse tan 10.46 or 84.5 for the angle

then in the x axis i got Fn sin θ - Ffr = mar for the sum of the forces. I substituted Ffr for µs x Fn and Fn = mg cos θ. I

I then had Fn sin θ - µs mg cos θ = mar

I divided mass from both sides and divided both sides by m.

I then for ar substituted v^2/r

Then I isolated µs by dividing cos θ and subtracting Fn sin θ

So I then had µs = V^2/r x cos θ - Fn sin θ

I plugged everything in and I got 9015, I know this wrong just by looking at it, the back of the book says .22, I am completely clueless, so if anyone could help, I'd greatly appreciate it. Sorry if it is a little confusing.