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Homework Help: Rolling Friction and Bicycle Tires

  1. Feb 5, 2006 #1
    my teacher Never went over this in class. ever. please help, thanks

    Two bicycle tires are set rolling with the same initial speed of 3.70 m/s along a long, straight road, and the distance each travels before its speed is reduced by half is measured. One tire is inflated to a pressure of 40 psi and goes a distance of 18.4 m; the other is at 105 psi and goes a distance of 94.0 m. Assume that the net horizontal force is due to rolling friction only and take the free-fall acceleration to be g = 9.80 m/s^2. What is the coefficient of rolling friction ur for the tire under low pressure?
     
  2. jcsd
  3. Feb 5, 2006 #2
    i tried to use this formula:

    ur= v/[(d/v) x g]

    and got

    ur=.075, but it said i was wrong

    ^ what exactly does it mean to be off by a constant?
     
    Last edited: Feb 5, 2006
  4. Feb 5, 2006 #3
    anyone?

    :frown:
     
  5. Feb 5, 2006 #4

    Hootenanny

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    Use the kinematic formula [itex]v = u + at [/itex] to obtain an acceleration. Then equate this with the force in [itex] F_r = \mu R [/itex]
     
  6. Feb 5, 2006 #5
    hmm but the problem is that i dont have [itex]u[/itex]; that is actually what im looking for
     
  7. Feb 5, 2006 #6

    Hootenanny

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    Yes you do, [itex]u[/itex] refers to the intial velocity. [itex]\mu[/itex] is the coeffiecent of friction. Sorry for the different symbols, its just the notation I'm used to.
     
  8. Feb 5, 2006 #7
    o i see, but i still dont have time. and i dont really get what that "R" refers to. if its radius, i didnt get it in this problem
     
  9. Feb 5, 2006 #8

    Hootenanny

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    R is the normal reaction force, which is the product of the mass and the gravitational field strength.
     
  10. Feb 5, 2006 #9
    i still dont understand since im not given mass
     
  11. Feb 6, 2006 #10

    Hootenanny

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    Masses will cancel, this is the same process you used for the boy/swing/inclined plane question.
    [tex] ma = \mu mg [/tex]
     
  12. Oct 17, 2007 #11
    so which equations did you use?
     
  13. Sep 30, 2008 #12
    How do you know what time is? when using v = v + at..
     
  14. Sep 30, 2008 #13

    Hootenanny

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    Looking back on this thread from two years ago, it would have been more appropriate to use the equation v2 = u2+2as. I don't know why I suggested the original one.
     
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