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Rotational KINEMATICS! (confusing)

  1. Nov 2, 2008 #1
    1. The problem statement, all variables and given/known data
    a) A 1.79 kg toy train accelerates constantly from 0.82 m/s to 3.43 m/s in 0.479 revolutions while traveling around a circular track of r 16.7 cm. Find:

    - α, magnitude of the angular acceleration.


    2. Relevant equations
    [​IMG]
    [​IMG]


    3. The attempt at a solution
    1. I first tried getting θ=(.479)(2pi)=3.009
    2. Then I found both the ωf and the ωo by finding the frequencies... I did this by first finding the distence covered by the partial revolution then using the velocity. I did this for both the ω's...
    3. Then i simply used the kinematic analog equation for rotational bodies and got α to be .00656 rad/sec2 and this came out to be wrong
    Is there a flaw in my reasoning
    Thank You
     
  2. jcsd
  3. Nov 2, 2008 #2

    Doc Al

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    Staff: Mentor

    I don't quite understand this step. Angular and tangential speeds are related by v = ωr.
     
  4. Nov 2, 2008 #3
    Isn't w-2pi(f)
     
  5. Nov 2, 2008 #4

    Doc Al

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    Staff: Mentor

    Do you mean does ω = 2pi(f)? Sure, you could think of it that way, but I don't see the point. You are given the linear speeds and the radius, so the angular speeds can be found immediately. (But, done correctly, you should get the same answer either way. Does your method give you the same answer?)
     
  6. Nov 2, 2008 #5
    Ooh so after I find the angular velocity I would just Use the equations to find alpha??

    And can you also explain why the tangental and angular velocities are related by v=omega (r)... Will an object traveling at 5 m/s linearly be going at 2.5 rad/s because it's going around a circle with radius 2?
     
    Last edited: Nov 2, 2008
  7. Nov 2, 2008 #6

    Doc Al

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    Staff: Mentor

    Sure.
    Yes.

    Read this: Rotational Quantities
     
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