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Homework Help: Stuck please help

  1. Aug 24, 2007 #1
    1. The problem statement, all variables and given/known dataWhat is the area, and its approximate uncertainty, of a circle of radius 3.9 104 cm? (Hint: Assume an uncertainty in the radius of 0.1 104 cm. Use the correct number of significant figures in your answers.)

    2. Relevant equationsI really don't know

    3. The attempt at a solutionThere's been a lot and scattered on paper...so I don't have one
  2. jcsd
  3. Aug 24, 2007 #2
    what's the area of a circle?
  4. Aug 24, 2007 #3

    and I did that and it wasn't the right answer...
  5. Aug 24, 2007 #4
    is that 14 in "14r^2"

    it should be pi.r^2
  6. Aug 24, 2007 #5


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    I can't read either one of you. What is a radius "3.9 104 cm" and why should "3.14r^2" be taken to have "14" in it? Is my browser rendering things wrong? Oh, yeah and since when are we using '.' for multiplication as in "pi.r^2"? You may be confusing each other.
    Last edited: Aug 24, 2007
  7. Aug 24, 2007 #6
    oops sorry..
    I thought 3 is a number (like those question numbers)..

    edit: I need to get a sleep :zzz:
  8. Aug 24, 2007 #7


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    Error propoagation is to do with how much effect errors have in the calculation.
    Simple example speed, if I know the distance to 10% and the time to 10% then the biggest error I could have in speed is 20% ( try some numbers if you aren't sure why)
    Whre two numbers are multiplied the percentage errors add.

    In area if I know the length to 10% and the width to 10% the worst error I could have is 20%.
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