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Related Rates and Circles

  1. Nov 7, 2013 #1

    Qube

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    Gold Member

    1. The problem statement, all variables and given/known data

    The circumference of a circle is increasing by 4 inches per second. What is the rate of change of the diameter with respect to time if the radius is 2 inches?

    2. Relevant equations

    C = 2∏r = ∏d.

    3. The attempt at a solution

    dC/dt = 4 = ∏dd/dt.

    dd/dt = 4/∏

    Is this it? It seems as if the information given about the radius is irrelevant.
     
  2. jcsd
  3. Nov 7, 2013 #2

    tiny-tim

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    Science Advisor
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    Hi Qube! :smile:
    yup! :biggrin:
     
  4. Nov 7, 2013 #3

    Mark44

    Staff: Mentor

    Yes, this is it. The circumference is a constant multiple of the diameter, so the rates of change of circumference and diameter are also going to be constant multiples of one another.
     
  5. Nov 7, 2013 #4

    Qube

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    Gold Member

    Alright, thanks guys. Thanks for the explanation; this provides an easy way to check!
     
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