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Homework Help: Missed my class and don't know how to even begin.

  1. Feb 13, 2012 #1


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

    a 100kg bicycle and rider initially move at 16 m/s up a 15 degree hill. The rider slams on the brakes and skids to rest. The coefficient of friction is (0.8, 0.7)

    2. Relevant equations
    I have a few but nothing to do with a coefficient of friction.
    The last ones given to me where like
    MVi + ƩF(Δt) = MVf

    3. The attempt at a solution
    I can' make any since I was sick for class. I'm sure the professor was supposed to give at least a hand out with some explanation. So could someone at least give me a idea what I have to look up online that will help me get started on this problem?
  2. jcsd
  3. Feb 13, 2012 #2
    What exactly are you trying to solve for? I'm guessing time?
  4. Feb 13, 2012 #3


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    Gehh sorry. Why do I keep forgetting that?
    a. How far does the bike skid?
    b. What was the elapsed time before the bike stops skidding?
  5. Feb 13, 2012 #4
    This is what I have to help so far.

    (100kg)(16m/s) + ƩF(Δt) = 0

    ƩF = (-mg sin(15) + uFn)
    →ƩF = (-9.8 x 100kg x sin(15)) + u( 100 x 9.8 x cos 15)

    →ƩF = -1232.877407

    (100kg)(16m/s) + (-1232.877407)(Δt) = 0

    1600 = (1232.877407)(Δt)

    Δt = 2.59

    I'm not sure if it is right, I might have forgotten a few things. Mainly...how to find ƩF

    Please correct me! I'm only a freshman.
    Last edited: Feb 13, 2012
  6. Feb 13, 2012 #5
    The basics are, 2 forces act on the bike:-
    Friction=Normal force * coefficient of KINETIC friction = (mg cosθ)*k
    gravitational force=mg sinθ

    From this info, find acceleration

    use v2-u2 =2as to find distance
    use v=u+at to find time.

    I'm not sure there are no other factors. Pls check!!
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