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Incline plane question

  1. Jul 13, 2008 #1
    1. The problem statement, all variables and given/known data

    Starting from rest, a cyclist coasts down the starting ramp at a professional biking track. If the ramp has the minimum legal dimensions(1.5 m high and 12m lomg) find
    a) the acceleration of the cyclist ignoring friction

    b) the acceleration of the cyclist if all sources of friction yield an effective coefficient of friction = .11

    c)time taken to reach the bottom of the ramp, if friction acts as in (b)

    2. Relevant equations

    My concern is the part a.
    V1= 0
    v2= ?

    I cant use Newton's 2nd law to find the a because the mass is not given nor the force.
    I looked at all kinematic equation and none of them works as well...so how do i approach solving this problem?
  2. jcsd
  3. Jul 13, 2008 #2
    The mass does not matter here.... It may get cancelled in the equations itself.
    Also try and upload a figure of the problem.
  4. Jul 13, 2008 #3
    no figure was given in the question
  5. Jul 13, 2008 #4


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    Homework Helper

    You know the height of the starting point 1.5m and you know the length of the starting ramp 12m and you know the value of gravity. 9.8m/s^2. You should be able to develop what the value of the constant acceleration is on the cycle shouldn't you?
  6. Jul 13, 2008 #5
    i dont get it...how?
  7. Jul 13, 2008 #6
    Firstly the dimensions of the ramp give the angle of inclination of the ramp. If the height is [tex]\var H[/tex] and the length of the ramp be [tex]\var L[/tex], then [tex]tan\vartheta=\frac{\var H}{\var L}[/tex]
    The particle model can be used here.
    Let the mass of the particle be [tex]\var m[/tex]
    Then observing the equilibrium perpendicular to the ramp,
    [tex]\var N = \var mg cos \vartheta[/tex]
    and along the ramp
    [tex]mg sin \theta - \mu mg cos\theta = ma[/tex]
    [tex]a=g sin \theta - \mu g cos\theta [/tex]

    which is independent of [tex]m[/tex]
  8. Jul 13, 2008 #7
    thank you. is the answer
    1.2 m/s^2 for part a and .13m/s^2 in part b?
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