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Homework Help: Calculating work using vectors.

  1. Feb 7, 2009 #1
    1. The problem statement, all variables and given/known data

    Calculate the work done if a 25N force acting in a direction of vector (2,3,-1) moves an object from P(2,-3,1) to Q(5,0,2).

    2. Relevant equations

    Work = Force (dot) Displacement

    3. The attempt at a solution

    Well force is 25N. But as for displacement, do I just find the displacement of the points P and Q, but then whats the direction vector (2,3,-1) for? I'm just a bit confused on this.
  2. jcsd
  3. Feb 7, 2009 #2


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    The displacement is going to be the vector Q-P. The direction vector is what direction the force is pushing on the object... you use the 25N part to determine what the magnitude of the force vector is. Then you take the dot product of that vector and Q-P
  4. Feb 7, 2009 #3
    The direction vector gives you the direction of the 25N force vector. The force vector is just the magnitude of the force times the unit normal in the direction of the force. You should be able to calculate the unit normal of the direction vector (2,3,-1).
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