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Homework Help: Friction Forces and max braking force

  1. Sep 18, 2007 #1
    1. The coefficient of static friction between the tires of a car and a dry road is .62. The mass of the car is 1500 kg. What is the maximum braking force is obtainable:
    a. horizontal to the road.
    b. on an 8.6 degree downgrade?

    2. F=mA f(s)=M(s)N N=mg F=f(s)-mgsin(x)

    a. f(s)=.62(9.8)(1500)sin90=9114 N
    b. f(s)=.62(9.8)(1500)sin8.6=2198 N

    My problem is that "b" isn't correct, I checked the back of the book I was using and they got 9000 N. Can anyone show me how to do this problem? I know I suck at physics. Also, if possible, can anyone explain to me how to find the tension of a string? Thanks!
  2. jcsd
  3. Sep 18, 2007 #2


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    Science Advisor
    Homework Helper

    If horizontal is 90 degrees, then 8.6 degrees downgrade must be 81.4 degrees. Most people would probably call horizontal 0 degrees and use a cos instead of sin. The tension on a string is "how much it pulls", sorry but that question is really vague.
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