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Homework Help: Shear stress on a tire from a puddle of water

  1. Oct 6, 2014 #1
    1. The problem statement, all variables and given/known data
    A car is moving at 65 mph and hits a puddle of water 1 inch deep. What is the shear stress on the tire from the puddle of water if the radius of the tire is 16 inches.
    r = 16 inches
    u = 65 mph
    y = 1 inch
    mu = viscosity = 2.344*10^-5 lbf*s/ft^2

    2. Relevant equations
    angular velocity:
    omega = u/r
    shear stress from fluid:
    tau = mu*u/y

    3. The attempt at a solution
    Velocity at the bottom of the tire is equal to the velocity of the car:
    u = omega * r
    shear stress on the tire:
    tau = mu*u/y
    I'm not sure about the velocity at the bottom of the tire.
  2. jcsd
  3. Oct 8, 2014 #2


    User Avatar

    Staff: Mentor

    Presumably the bottom of the tire is in contact with the road surface and not slipping, so its instantaneous velocity will be zero.
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