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Circular Motion

  1. Feb 27, 2009 #1
    1. The problem statement, all variables and given/known data

    A wheel 31.8 cm in diameter accelerates uniformly from 242 rpm to 380 rpm in 7.66 s. How far will a point on the edge of the wheel have traveled in this time?


    2. Relevant equations

    angle = initial angle +angular velocity(t) + .5(angular acceleration)(t)

    w=initial angular velocity +angular acceleration (t)

    and s=R*angle

    3. The attempt at a solution

    i tried plugging into the equations but i really dont know what to do
     
  2. jcsd
  3. Feb 27, 2009 #2

    LowlyPion

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    Homework Helper

    Not quite.

    θ = θo + ω*t + 1/2*α*t2

    Where θ is in radians.

    And there are 2π radians in a revolution.

    First convert your ω's to radians/sec from rpm and figure α and then you can figure your θ.

    To find distance ... x = θ *r
     
  4. Feb 27, 2009 #3
    I converted to rad/sec so its 25.34 and 39.79
    I found a = (39.79-25.32)/7.66 =1.886
    then I used θ = θo + ω*t + 1/2*α*t2
    and did θ = 0 + 25.34*7.66 + 1/2*1.886*7.66 = 249.435

    So i got x=θR = 249.435(15.9) = 3966.01

    But this is wrong, is there something else I need to convert or calculate?
     
  5. Feb 27, 2009 #4

    LowlyPion

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    Homework Helper

    Without doing any other math I would note the diameter is .318m.

    Always, always stay in SI units wherever possible.
     
  6. Feb 27, 2009 #5
    Oh ok, that's what I did wrong. I got it. Thank you!
     
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