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Homework Help: Finding pulley diameter with speed in rpm

  1. Nov 25, 2016 #1
    1. The problem statement, all variables and given/known data

    In a pulley system, pulley A is moving at 1,500 rpm and has a diameter of 15 in. Three pulleys, B, C, and D, all of different sizes, are attached to a single output axle. Speed and torque output are changed within the system by moving the drive belt between pulleys B, C, and D.

    A speed of 2,000 rpm is required when the drive belt is connected to pulley C. What is the diameter of pulley C?

    The question is here, how do I find the diameter? I don't know the input or output speeds.

    2. Relevant equations


    3. The attempt at a solution


    (not sure if this is right)
  2. jcsd
  3. Nov 25, 2016 #2


    User Avatar
    Science Advisor

    You sure about that?...

    There's no equality so that's not an equation.
    You're looking for an equation that relates the diameter of a pair of pulleys with their rotational speed, check your notes and/or textbook. You know both RPM's and one diameter so can solve for the single unknown; the second pulleys diameter.
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