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# If a curve with a radius of 79m is perfectly banked for a car traveling 71 km/h , what must be the...?

If a curve with a radius of 79m is perfectly banked for a car traveling 71 km/h , what must be the coefficient of static friction for a car not to skid when traveling at 89km/h?

Yes, It is asking for the coefficient of static friction

### 3 Answers

- SteveLv 77 years agoFavorite Answer
Bank angle Θ = arctan[v²/(Rg)] = 26.675°

For 89 k/h,

µ = [V² - RgtanΘ]/[Rg + V²tanΘ] = 0.205

Source(s): Free body diagram My 'cheat sheet' of physics formulae - Anonymous7 years ago
trick question? does it specifically say static friction?

mu N is friction force, mu N r is frictional torque.

so if friction is = to the force outward, then mu N r = m a r

- CuglierLv 67 years ago
It is perfectly banked at v=71km/h=19.72m/s..R=79m

Fcf=f....Fcf=Fcp=mv2/R....slope "α"

f=N*µ...N=mg cosα *µ.......µ.=tanα =senα /cosα

m*v2/R=mg*cosα *µ...v2/R=g.senα ...sen α =v2/Rg = 0.5

then α =30° ...µ=tan α =0.5773

Now at v=89km/h=24.72 m/s

the coefficient of static friction is:

mv2/R =mg*cosα*µ .......µ.st=v2/(Rg* cos30°)=0.91 Answer

µ= 0.5773<µ.st= 0.91

Hope this helps

Cuglier

Source(s): It