1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Friction contradiction

  1. Feb 23, 2008 #1
    1. The problem statement, all variables and given/known data

    What is the smallest radius of an unbanked (flat) track around which a bicyclist can travel if her speed is 29 km/h and the coefficient of static friction between tires and track is 0.29?

    2. Relevant equations

    coefficient of static friction = (f of maximum static friction / Normal force)

    fnet = ma = m * v^2 / r

    3. The attempt at a solution

    If an object is moving, isn't their just kinetic friction? I get that the normal force is the acceleration, but how can there possibly be a maximum static friction at this point?

    Here's what I've got:

    29km/h = 8.0556 m/s

    .29 = fstatmax / a, therefore a = fstatmax / .29

    Fnet = m* a = m * (v^2 / r)
    Fnet = a = v^2 / r
    fstatmax / .29 = (8.0556)^2 / r

    Thanks for any help!
  2. jcsd
  3. Feb 23, 2008 #2
    In case of tyres, the bottom-most point is instantaneously at rest. That's why static friction.


    solve to get r.
  4. Feb 23, 2008 #3
    thank you for the help!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook