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Homework Help: Grade 12 physics help please

  1. Oct 3, 2013 #1
    Grade 12 physics help please!!

    1. The problem statement, all variables and given/known data

    2. A car is travelling along the QEW. It leaves the highway on a turn that has a radius of 90.0m.
    a. If the coefficient of maximum static friction between the tires and the road is 0.89, and typical speeds are 100km/h, what is the minimum angle the road needs to be banked at so the car doesn’t go sliding off the road?
    b. If the coefficient of maximum static friction was reduced to 0.40 because of rain or an oil spill, what is the new minimum angle that the road should be banked at to avoid sliding off the road?

    3. A road is banked at an angle of 12° and the radius of the curve is 75m. If the coefficient of friction between tires and dry concrete is 0.9 and it reduces to 0.6 in rain, what do you feel the posted speed limit should be?

    2. Relevant equations

    Fnet = mac

    ac = mv2/r

    ac = 4∏2r/T2

    3. The attempt at a solution

    for number 2, I just don't know. :(

    for the third, I think I can use mv2/r, but I'm not sure how to solve without mass or velocity.

    Any help would be greatly appreciated!
  2. jcsd
  3. Oct 3, 2013 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    PF prefers if you post one HW problem per thread.

    You also must try to solve the problem before getting help.
  4. Oct 3, 2013 #3


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    Staff: Mentor

    Anytime you're working with multiple forces start in the usual way, with a free body diagram identifying all the forces acting. Decide what conditions must occur for the car not to slide sideways (in particular, the critical point where the car is just about to start sliding).

    If you think that certain values are missing (like a mass or a velocity) just leave them in symbolic form. If it turns out that they're not required to solve the problem, eventually they'll cancel out as you work through the math. In #3 you're actually looking for a velocity, so no surprise there that it's "missing" :smile:

    And as SteamKing says above, some effort on your part will be required before help with solving your problem can be given. We need to see your attempt so that we can know how to help you.
    Last edited: Oct 3, 2013
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