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Simple Pulley Question

  1. Sep 2, 2008 #1
    A narrow belt is used to drive a 20.00-cm diameter pulley from a 35.00-cm-diameter pulley. The centers of the two pulleys are 2.000 m apart. How long must the belt be if the pulleys rotate in the same direction? In opposite directions?

    I am sure the solution to this problem is very simple, but I just cannot seem to figure out how to even begin this problem.Any help would be appreciated.
     
  2. jcsd
  3. Sep 3, 2008 #2
    I think you just need to find the hypotenuse using trigonometry.
     
  4. Sep 3, 2008 #3

    Redbelly98

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    Solving this begins with drawing a picture of the wheels and belt.
     
  5. Sep 3, 2008 #4
    well of course that would be the obvious thing to do. Once i have it drawn I am guessing I need to form a right triangle? Simply by extending a tangent line from one pulley to the other on top and bottom? From here i am stuck. I know that the center is 2 cm but how do you calculate for the belt wrapping around the pulley itself? Would that be arc length or something?
     
  6. Sep 3, 2008 #5

    tiny-tim

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    Hi ur5pointos2sl! :smile:
    Yes, that's arc-length! :smile:
     
  7. Sep 4, 2008 #6

    Redbelly98

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    Okay, guess I took you too literally when you said you didn't know how to begin.

    Pretty much. Draw simple shapes like right triangles, rectangles, and/or circles to figure things out. Yes, the length of belt portion wrapping around the pulley is an arc length; you'll need to figure out the angle involved using geometry and trig.
     
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