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Math Help - angular acceleration

  1. #1
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    angular acceleration

    A ceiling fan is turned on and reaches an angular speed of 120 rev/min in 20s. It is then turned off and coasts to a stop in an additional 40s. What is the ratio of the avg. angular acceleration for the first 20s to that of the last 40s?
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  2. #2
    MHF Contributor arbolis's Avatar
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    For the first 20 seconds, the modulus of the angular acceleration is twice the one for the last 40 seconds. (head calculus : it takes twice the time to slow down than it took to reach it's maximum angular velocity.)
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  3. #3
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    ignoring the signs of each angular acceleration, the ratio is 2 : 1

    think about why that is true.
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