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Angular acceleration of a tire...not sure how to find radius

  1. Sep 30, 2015 #1
    1. The problem statement, all variables and given/known data:
    Your car tire is rotating at 3.5 rev/s when suddenly you press down hard on the accelerator. After traveling 200 m, the tire’s rotation has increased to 6.0 rev/s. What was the tire’s angular acceleration? Give your answer in rad/s2.

    2. Relevant equations:
    2αΔΘ=ωf2i2

    3. The attempt at a solution:
    2α(uhh)=(37.7 rad/s)2-(22.0 rad/s)2
    We have 200m as a distance. With the absence of a tire's diameter, I tried (200 m)/(2πr rads) but again I don't know the radius. The book's solution manual uses ΔΘ=Δx/r and then simply states that the tire's radius is 32cm. I have no idea where this number came from.
     
  2. jcsd
  3. Sep 30, 2015 #2

    tony873004

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    leave delta phi as x / r. Also, don't translate rev / second into rad /s. Instead, translate rev into 2 pi r, and you'll find the r's cancel.
     
  4. Sep 30, 2015 #3
    I don't understand. Isn't the definition that rev=2π?
     
  5. Oct 1, 2015 #4

    haruspex

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    There is only one variable which involves the dimension of distance. That makes it useless. There is simply not enough information.
    Breadsticks, it looks like they forgot to tell you the radius.
     
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