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My brain is fried and I need help

  1. Aug 12, 2008 #1
    I'm doing some problems for physics at the end of one the chapters and I get to a question that asks
    "At what temperature does Fahrenheit and Celsius have the same numerical value?"

    Now the answer is -40, but I'm not sure how this answer was established. Between class, lab and study time, I've been pouring over physics for the last 7 hours and I'm toasted. I have a feeling that the answer is pretty simple, but I can't seem to get it. Does anybody have any answers?
  2. jcsd
  3. Aug 12, 2008 #2


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    Well you just have to equate the temperature in one scale to the formula for conversion in the other scale and solve the unknown, right?
  4. Aug 12, 2008 #3


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    from Dan Monaghan:
    That is simple first-year highschool Algebra. You barely need any physics knowledge at all. F: fahrenheit, water boils at ~212, freezes at ~32. C: Celsius, water boils at 100, freezes at 0. Find the linear equation.
  5. Aug 12, 2008 #4
    F = (9/5)C + 32
    We're looking for an F where F = C, so

    F = (9/5)F + 32

    -(4/5)F = 32

    F = -32 * 5/4

    F = -40

    So at -40 degrees the Celsius value is the same as the Fahrenheit value.
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