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Homework Help: Rotational Motion Question

  1. Jan 8, 2012 #1
    1. The problem statement, all variables and given/known data
    A rotating bicycle wheel has an angular speed of 2.84 rad/s at some instant of time. It is then given an angular acceleration of 1.75 rad/s2. A chalk line drawn on the wheel is horizontal at t = 0. What angle does this line make with its original direction at t = 1.77 s?

    2. Relevant equations

    The rotational kinematics equations.

    3. The attempt at a solution

    Using the equation:

    Δθ = ωt + (1/2)(ang. accn)t2

    = (2.84)(1.77) + 0.5 (1.75)(1.77)^2
    = 7.77rad

    I can't get it right. I have a feeling I have to use the angular acceleration to change the angular velocity, but I can't figure out how to do this. It's probably something really silly so if someone could point out what I'm doing wrong it would be much appreciated.
     
    Last edited: Jan 8, 2012
  2. jcsd
  3. Jan 8, 2012 #2
    Angular acceleration is 1.75, not 1.62
     
  4. Jan 8, 2012 #3
    Sorry, typo. Fixed now. Answer is still wrong.
     
  5. Jan 9, 2012 #4
    Anybody?
     
  6. Jan 9, 2012 #5
    Maybe you should subtract 2pi from the answer?
     
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