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Cranks and Pistons

  1. Feb 1, 2005 #1
    Hello all

    I was given a problem involving cranks and pistons. I do not understand the exact question, but it involved an oblique triangle where you had to apply the Law of cosines. Lets say you are given [tex] \theta = \frac{\pi}{4}, x=7, c = 11 [/tex] where [tex] c [/tex] where c is the hypotenuse and [tex] \frac{dx}{dt} = 200 [/tex]. Find the rate of change of the piston.

    So here it is:

    [tex] c^2 = a^2 + b^2 - 2ab\cos C [/tex]
    [tex] a^2 = b^2 + c^2 - 2bc\cos A [/tex]
    [tex] b^2 = a^2 + c^2 - 2ac\cos B [/tex]

    Ok so how would I solve for the change of the piston? Would I just find the derivative of the first Law of Cosine expression and substitute in the values?
  2. jcsd
  3. Feb 1, 2005 #2


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    Okay,what's the connection betweent the 4 variables:a,b,c & x?? :confused:

  4. Feb 1, 2005 #3


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    What is x and what in the world is "the change of the piston"? (How does a piston change?)
  5. Feb 1, 2005 #4
    sorry I meant to say the rate of change of the piston . [tex] x [/tex] is one of the sides of the triangle.
  6. Feb 1, 2005 #5


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    Still doesn't make too much sense... :grumpy: What about a,b,c ???What are they...??

    HINT:Post the initial problem's text in original form... :grumpy:

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