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Homework Help: Finding the work done using force vectors in 3 dimensions

  1. Mar 13, 2013 #1
    1. The problem statement, all variables and given/known data
    Find the work done by a force acting in the direction 2i - 5j + k in moving a particle from (3, 3, 1) to (1, 2, 4).

    2. Relevant equations

    3. The attempt at a solution
    I just found the displacement vector (2,1,-3) and did the dot product with the force vector.
    So my answer as an integer, was negative 4.
    Does that sound correct?
  2. jcsd
  3. Mar 13, 2013 #2


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    Homework Helper

    The question is somewhat imprecise; the force doesn't just act in that vector direction, it is given by that vector. Force has direction and magnitude - if they only meant that vector to represent the direction, they need to state the magnitude separately.

    You got a negative answer because you took the wrong direction for the displacement vector. What is displacement? Is it final minus initial position or vice versa?
  4. Mar 13, 2013 #3
    oh yeah lol, its final minus initial
    so my answer should be positive 4 right?
  5. Mar 13, 2013 #4


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    Homework Helper

    Yes. Units would be nice, but if you weren't given any for the force and distance, what can you do?
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