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Homework Help: Angular Speed of Tires

  1. Mar 30, 2012 #1
    1. The problem statement, all variables and given/known data

    The tires of a car have a radius of 31 cm. What is the angular speed of these tires when the car is driven at 12 m/s?

    2. Relevant equations

    w=θ/t

    3. The attempt at a solution

    θ=d/r
    θ=d/31
     
  2. jcsd
  3. Mar 30, 2012 #2

    berkeman

    User Avatar

    Staff: Mentor

    Maybe you could try to expand a bit on your attempt at the solution? You didn't even include the velocity of 12m/s in your attempt.

    What is the circumference of tires that have a radius of 31 cm? Be sure to keep units consistent -- usually you convert it all into meters.
     
  4. Mar 30, 2012 #3
    circumference=194.77
    12=wr
    im not sure if that is the way to use the 12
     
  5. Mar 30, 2012 #4
    The tangental speed of the tires are the same as the speed of the car. This is because there is assumed no slipping of the tires - they are always in "non-moving" contact, just rolling. In other words, the distance the car travels in time t is equal to the distance gone around the circumference of the tires in time t. Think of the tire laying out a "print"/line as its contact point rolls some distance.

    Thinking about this should help you solve this problem.
     
  6. Mar 30, 2012 #5
    so 194.77=the distance traveled
    so θ=6.2829
    so w=.3871 does this seem right?
     
  7. Mar 30, 2012 #6
    Did you make sure to convert the radius from cm to m?
     
  8. Mar 30, 2012 #7
    after i converted i got 39 but it says that is incorrect
     
  9. Mar 30, 2012 #8
    Maybe you have over rounded?
     
  10. Mar 30, 2012 #9
    i went to four significant figures in each calculation but i had to give my answer in two
     
  11. Mar 30, 2012 #10
    Ok. So you have the answer now? :)
     
  12. Mar 30, 2012 #11
    its still saying my answer is incorrect
     
  13. Mar 30, 2012 #12
    The angular speed should be ~38.71 rad/s as you had before converting cm to m.
     
  14. Mar 30, 2012 #13
    got it! thanks!
     
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