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Homework Help: Having trouble with friction, incline problems

  1. Sep 28, 2004 #1
    This question was a two parter

    A car of mass 422 kg travels around a flat,
    circular race track of radius 178 m. The co-
    efficient of static friction between the wheels
    and the track is 0.135.
    The acceleration of gravity is 9:8 m=s2 :
    What is the maximum speed v that the car
    can go without flying off the track?

    I got vmax as 15.3458 m/s

    The same car now travels on a straight track
    and goes over a hill with radius 200 m at the
    top.
    What is the maximum speed that the car
    can go over the hill without leaving the road?

    I'm not sure how to go about tackling that problem, I tried just substituting 200 m in for the radius but that doesn't work.

    This one was also a two parter

    A civil engineer is asked to design a curved
    section of roadway that meets the following
    conditions:
    With ice on the road, when the coefficient of
    static friction between the road and rubber is
    0.23, a car at rest must not slide into the ditch
    and a car traveling less than 50 km=h must
    not skid to the outside of the curve.

    At what angle should the road be banked?

    I got the angle to be 12.95

    What is the minimum radius of curvature of
    the curve?

    I tried using tan(theta)=v²/rg, but again I was wrong.

    Any help would be greatly appreciated.
     
  2. jcsd
  3. Sep 28, 2004 #2

    Pyrrhus

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    Homework Helper

    Your first problem is correct.

    Your second problem requires you to think about the centripetal force, give it some thinking.

    (Oh a fellow Civil engineer problem :cool: ) On your third problem the formula you used works only without friction, try solving it with friction.
     
  4. Sep 28, 2004 #3
    I'm still stuck on both of them, our teacher didn't talk about finding centripetal force with uniform circular motion, can you give another hint?
     
  5. Sep 28, 2004 #4

    Pyrrhus

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    Homework Helper

    What are the forces acting at the top of the hill??
     
  6. Sep 28, 2004 #5
    Nevermind, he just used different word, thanks for your help
     
  7. Oct 12, 2006 #6
    How do you do the 2nd equation?
     
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