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Homework Help: Pulley and rotation problem

  1. Sep 29, 2008 #1
    1. The problem statement, all variables and given/known data
    A tractor has a belt pulley diameter of 10 inch operating at 1100 revolutions per minute. The pulley is connected by a belt to another machine that needs to operate at 650 rpm. What size should the pulley be on the second machine?


    2. Relevant equations
    2Pi*r



    3. The attempt at a solution
    I don't really know where to start. I know that a wheels circumference is 2Pi*r
    The first wheel is 10 inches so
    2*Pi*5 inches = 1100rpm
    if the second wheel has to operate at 650
    can I get it by 650/2pi=103 inches?
     
  2. jcsd
  3. Sep 29, 2008 #2

    Integral

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    Set up a simple ratio.

    [tex] \frac {1100} {10} = \frac {650} x [/tex]
     
  4. Sep 29, 2008 #3
    thank you
     
  5. Sep 29, 2008 #4
    I'm still a bit unclear. Sorry.
    If I set up a ratio
    1100/10=650/x
    I get an answer of 5.9
    I need the second wheel to rotate slower but if it is smaller wont it spin faster?
     
  6. Sep 30, 2008 #5
    I tried this again.
    This seems to work.

    driven pulley rpm= drive pulley rpm * drive pulley diameter/driven pulley diameter

    650rpm=1100rpm*10inch/x
    650x=11000
    x=16.923 inch diameter for the pulley
     
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