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Homework Help: Banked Curve- find the Velocity when static MU=0

  1. Oct 15, 2008 #1


    (Green means correct)

    1. The problem statement, all variables and given/known data
    A a 14600 kg *rubber-tired car moves on a concrete highway curve of radius 71 m is banked at a 12° angle.

    (a) What is the normal force acting on the car?

    (b) What is the speed with which the car can take this curve without sliding? (Assume s = 0.)

    2. Relevant equations

    2nd law statements

    a= V^2/ r

    3. The attempt at a solution

    So I began part a by drawing force diagrams and then 2nd law statements. I was left with:

    n= mg/ cos@
    n= (14600)/ cos12

    That was correct. I then attempted to move along to part b. I began this by saying that the total force is static friction, therefore:

    Fs(the maximum)= Mass(V(maximum)^2)/r
    V^2= (mu)*gr

    However, with mu=0 then this all totals to zero. I'm not sure how to get around this. Plus, logically if the coefficient of static friction is zero, then no matter what wouldn't the car slide??

    Thanks in advance!

    Last edited: Oct 15, 2008
  2. jcsd
  3. Oct 15, 2008 #2
    My only interpretation of this question is this:

    - The car will slide DOWN side ways because there is no friction on the road. If he went super-fast (over-exaggeration of course), the car would slide UP because of the effective weight from it's the centrifugal force (not centripetal). So you are asked for the speed at which the car will not slide up or down the bank.

    That is my interpretation of the question.

    Best Regards,
    Sam :smile:
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