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Homework Help: Particle is located a distance x meters

  1. Sep 12, 2013 #1
    1. The problem statement, all variables and given/known data

    When a particle is located a distance x meters from the origin, a force of cos(PIx/3) newtons acts on it. How much work is done in moving the particle from x = 1 to x =2? Interpret your answer by considering the work done from x =1 to x = 1.5 and from x = 1.5 to x = 2

    2. Relevant equations

    So the integral isn't a problem.
    If you graph this function I'm sure you know the sign change where cos(pix/3) dips below the x axis at 1.5. I'm just wondering if I should give my answer as the sum of the neg work and positive work. If the work is negative doesn't it mean it is on the opposite direction? But I still say oh this has done. Neg + pos work

    3. The attempt at a solution
  2. jcsd
  3. Sep 12, 2013 #2


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    Science Advisor

    Since they are talking about "work" I think they expect a more "physical" explanation. Here, you are doing work from x= 1 to x= 3/2 but then works is being done from x= 3/2 to 2. It's like doing work to push an object to the top of a hill, then getting work out by allowing the object to run down the other side.
  4. Sep 12, 2013 #3
    Ah so rolling a rock up a hill and letting it roll the other side? Do I consider the negative work as postive so I add the area above the graph and the area below for total work?
  5. Sep 12, 2013 #4


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    No, you do NOT "consider the negative work as positive". The total work done is the "area above the graph minus the area below the graph"- in other words precisely [itex]\int_1^2 f(x)dx[/itex]
  6. Sep 12, 2013 #5
    Yeah so you do no work then with this problem. The integrals are equal above and below
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