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Homework Help: Work with a variable force

  1. Apr 26, 2012 #1
    1. The problem statement, all variables and given/known data
    An object is moved from 0 to 9 meters with a force varying according to the function F(x)= 50(5-square root x). What is the work done.

    2. Relevant equations

    3. The attempt at a solution

    I tried to take the integral and evaluate it from 0 to 9. I get 1350J no matter what I do, which is not correct. The correct answer is given as 1700 J. Any help?
  2. jcsd
  3. Apr 26, 2012 #2


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    Staff: Mentor

    It sometimes happens that the given "answer" is not correct. If you show your work in detail then we can see if your method produces a correct result.
  4. Apr 26, 2012 #3
    I will only say that F(x) is not always positive.
  5. Apr 26, 2012 #4
    Yes, but it is positive over the spatial domain in question. Furthermore, since this is a conservative force, the work done from the starting point to the ending point will be independent of the path.

    My calculation yields the same number as the OP's.
  6. Apr 26, 2012 #5

    Yeah you are right..sorry . This must definitely be the most useless hint ever ! :P
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