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Homework Help: Rotational acceleration

  1. Oct 10, 2015 #1
    1. The problem statement, all variables and given/known data
    Moving at its maximum safe speed, an amusement park carousel takes 12 s to complete a revolution. At the end of the ride, it slows down smoothly, taking 3.5rev to come to a stop. What is the magnitude of the rotational acceleration of the carousel while it is slowing down?

    2. Relevant equations
    w2=wo2+2alpha theta

    3. The attempt at a solution
    plug in and get -pi/144 rad/s2 is this right???
  2. jcsd
  3. Oct 10, 2015 #2
    or -pi2/504 s-2
  4. Oct 10, 2015 #3
    When it moves with maximum speed, the angular velocity is ## \omega_i = \pi / 12. ## You want to stop it within ## 3.5 ## revolution, that is ## \theta_f - \theta_i = 7\pi ## and it have to be ## \omega_f = 0. ## Then, you can get the angular acceleration, ## \alpha. ##
  5. Oct 10, 2015 #4
    shouldn't the angular velocity be pi/6?
  6. Oct 10, 2015 #5
    Oh, yes I missed the factor ## 2##.
  7. Oct 10, 2015 #6
    Can you also help me check this one? You hold a small ice cube near the top edge of a hemispherical bowl of radius 100 mm. You release the cube from rest. What is the magnitude of its acceleration at the instant it reaches the bottom of the bowl? Ignore friction. is a=2g=19.6 m/s2
  8. Oct 10, 2015 #7


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    Which one?

    Always show your work in detail.
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