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Homework Help: What is the angular displacement of a thrown ball

  1. May 10, 2013 #1
    1. The problem statement, all variables and given/known data
    A ball is thrown to a man and reaches him in 60s. The ball curves because it is spinning at an average angular velocity of 330 rev/min on its way to the man's hands. What is the angular displacement of the ball

    2. Relevant equations

    3. The attempt at a solution
    I converted 330 rev/min to 17.279 rad/s
    but when I plug it into the equation I get 1,036.74... I feel like I'm missing a final step here but I don't know what I'm doing wrong.. please help
  2. jcsd
  3. May 10, 2013 #2


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    Hello, ashezb. Welcome to PF!

    Are you sure the time is 60s? That's one heck of a throwing arm :bugeye:

    Your conversion of 330 rev/min to rad/s does not look correct. Remember, there are ##2\pi## radians in one revolution.
  4. May 10, 2013 #3


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    Staff: Mentor

    Hi ashezb, Welcome to Physics Forums.

    How did you convert 330 rpm to radians per second? Can you write it out? (I ask because your value doesn't look right).

    Once you have the total angular distance, remember that the displacement should lie in the range 0 → ##2\pi##. How might you go about reducing (normalizing) the angle?
  5. May 10, 2013 #4
    Now that I really think about it 60s is one heck of a throw, but the question does say 60s

    Yes I did my conversion wrong. I used π in stead of 2π

    but I am still confused....these are the given answers
    a) 21 rad
    b) 20 rad
    c) 19 rad
    d) 17 rad
    e) 14 rad

    The only way I can make is work is to turn the seconds into 0.60 seconds in which case a would be correct.

    Thanx for being so welcoming and so helpful :)
  6. May 10, 2013 #5


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    Sounds good.
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