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Statics: Dimensionless Unit Vector

  1. Jan 14, 2017 #1
    1. The problem statement, all variables and given/known data
    Equation.PNG
    Question.PNG
    2. Relevant equations
    Unit Vector.PNG
    3. The attempt at a solution
    So I began by subtracting.
    (205-160)=55 i
    (495+128)=623 j
    Both of these vectors are in the positive direction. So if I divide the vector by its magnitude I should get an answer of 1 in the positive direction for both i and j.
    The online book lists the answers as R hat = 0.0720 i + 0.997 j . I guess I'm not sure how the book got these answers. I thought unit vectors always had a magnitude of 1 and their purpose was to determine the direction of the vector.
    Thank You!
     
  2. jcsd
  3. Jan 14, 2017 #2

    Doc Al

    User Avatar

    Staff: Mentor

    If each component had a magnitude of 1 then the vector would not be a unit vector!

    The unit vector does have a magnitude of 1. Given those components, find the magnitude of the full vector. What do you get?
     
  4. Jan 14, 2017 #3

    Mark44

    Staff: Mentor

    Minor point, but ##\vec{B} - \vec{A}## has units of lbs, and so would a unit vector in this direction. I'm puzzled by the instruction to "find a dimensionless unit vector" in this direction.
     
  5. Jan 14, 2017 #4

    Doc Al

    User Avatar

    Staff: Mentor

    If you divide by the magnitude (also in lbs) you can get a dimensionless direction vector.
     
  6. Jan 14, 2017 #5

    Mark44

    Staff: Mentor

    OK, that makes sense. Objection withdrawn...
     
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