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Math Help - Stuck on angular motion. need to find time, and not sure what......

  1. #1
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    Stuck on angular motion. need to find time, and not sure what......

    Stuck on an Angular Motion question.

    Basketball is spinning on top a finger. The angular velocity of the ball slows down from 18.5 to 14.1 rad/sec. During this time, the angular displacement is 85.1 rad. Determine the time it takes for this to happen.

    So theta is 85.1 rad,
    for the 18.5 and 14.1 do I subtract the two? to get omega?
    I am not sure and going thru my notes I can't find what I am looking for, so not sure what to do?

    Which formula do I use as well. wouldn't be w=theta/time?
    If someone can get me started would be great, thanks for looking.
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  2. #2
    MHF Contributor Unknown008's Avatar
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    Use:

    v^2 = u^2 + 2as

    to find the angular acceleration first.

    a = \dfrac{14.1^2 - 18.5^2 }{2(85.1)} = -0.843 rads^{-2}

    Now, use v = u+at

    18.5 = 14.1 - 0.843t

    t = 5.22 s
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  3. #3
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    Oh wow, thanks. I missed the first step. I was not sure if you had to find acc or not. THANK you for the help, it helps alot.
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  4. #4
    MHF Contributor Unknown008's Avatar
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    You're welcome!

    PHF doesn't have functional LaTeX, so I preferred answering here.
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