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Questions about Line Integrals

  1. Sep 18, 2005 #1
    Say we have a vector, lets use something simple like

    A = 2xyi + 3yzj

    Say we want to find the work done on a particle traversing a path, so we just add up the work done on each path. Let the path be:

    y = x^2 from x = 0 to x = 5
    y = 25 from x = 5 to x = 10
    now a final path from (10,25) to (10,35)

    How do I enter my limits in if Work = integral A • Ds ?
  2. jcsd
  3. Sep 18, 2005 #2


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    Science Advisor

    Write the path in parametric equations. Use the value of the parameter corresponding to the beginning and ending points.
    In this particular case, since y is a function of x, it is simplest to take x itself as the parameter. Write your integral entirely in terms of x and use the x values as limits of integration. Since your function changes at x= 5, you will probably want two integrals, one from 0 to 5, the other from 5 to 10.

    By the way, your force vector is A = 2xyi + 3yzj which includes "z" but you only have i and j and your path only includes x and y. Was that intentional?
  4. Sep 18, 2005 #3
    No, I was just making up a random vector.

    Must I do a parametization? Is it not possible just to plug in the change of x for the limits of dx and the change of y for the limits of dy for each seperate curve then add 'em up?
  5. Sep 19, 2005 #4


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    Homework Helper

    This may sometimes be possible, but in general it's not.
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