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Homework Help: Unwounding of a spool

  1. Nov 7, 2009 #1
    1. A spool of wire is rolled out along a level floor. If the radius of the spool is 48.0 cm and the spool makes 2.1 revolutions, what length of wire (in cm) is unwound?

    velocity = (angular velcity)(radius)

    2.1 rev * 2pie radians/rev. I know the revs will cancel and i will have 4.2pie radians

    Since velocity = Distance/time i will say time=1 min then i get distance=(48.0)(4.2pie) which is 201.6pie cm/min and i will divide this by 60 to get 3.36pie cm/sec

    Am i going in the right direction? I dont know if what i did so far is right or if im missing something, thanks in advance for the help this would really help me for the midterm i got on tuesday
  2. jcsd
  3. Nov 7, 2009 #2


    Staff: Mentor

    There's nothing in this problem that gives velocity or asks for it. All that's needed is the length of wire that unwinds from the spool.

    BTW, the name of this Greek letter, [itex]\pi[/itex], is pi, not pie. A pie is something you can eat.
  4. Nov 7, 2009 #3
    Mmm... I sure wish I had that many pies per second...

    A few hints:

    Find how much would be left behind with one revolution. This should be simple, and you have all the variables necessary. But the spool makes 2.1 revolutions. How much would then be left behind?

    You are making it more complex than it needs to be. Who cares how fast the thing goes? Besides, you don't have the information to do this. You only really need how far it went.
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