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Calculus Work Problem involving an integral?PLEASE HELP!?

The force (Newtons) with which 2 electrons repel each other is inversely proportional to the square of the distance (in meters) btwn them. a) if one electron is held fixed at the point (5,0), find the work done in moving a second electron along the x-axis from the origin to the point (3,0). the answer is 3k/10 where k is a constant i just need help setting up the integral thanks!

4 Answers

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  • Boozer
    Lv 4
    1 decade ago
    Favorite Answer

    Well, work is defined to be the integral of F dotted with dx.

    W = ∫F ∙ ds

    They beauty of this problem is that we're only moving in one dimension... Everything is always on the x axis!

    So the integral becomes

    W = ∫F ∙ dx = ∫F dx

    So, what's the force between the two charges???

    F = k * q1 * q2 / r².

    Since k * q1 * q2 is a constant... we'll call it P. k is an actual physical constant. r is the distance between the 2 particles

    So F = P/(5 - x)²

    and

    W = ∫P/(5 -x )² dx = P∫dx/(5 - x)² = P/(5 - x)

    x ranges from 0 to 3, so

    P/(5 - 3) - P/(5 - 0) = 3p/10

    My p is your k.

  • radne0
    Lv 5
    1 decade ago

    W = ∫ F dx

    "The force (Newtons) with which 2 electrons repel each other is inversely proportional to the square of the distance"

    tells you that

    F=k/d²

    "if one electron is held fixed at the point (5,0), find the work done in moving a second electron along the x-axis from the origin to the point (3,0)"

    tells you how to setup d and your limits of integration

    one electron starts at 0 and moves towards five so,

    d=(5-x)

    F=k/(5-x)² so

    Since, again, W = ∫ F dx and using "from the origin to the point (3,0)" to get the limits of integration

    W= ∫ k/(5-x)² dx from 0 to 3

    W = k ∫1/(5-x)² dx from 0 to 3

    To verify that it is 3k/10

    u = 5-x

    dx = -1 du

    W = -k ∫1/u² du from 5 to 2

    integrating -k [-1/u from 5 to 2]

    k [1/2 - 1/5]

    3k/10

  • ?
    Lv 4
    5 years ago

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  • 1 decade ago

    This is an extremely completed equation. Are you like in AP Calculas?? Omg...I'm in Honors Calculas and I've never done anything like this..Umm..Sorry

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