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Homework Help: Vector addition problem

  1. Dec 1, 2007 #1
    2cm N + cm W

    b. 5m S+ 8cm N

    c. 30m/s W+ 50m/s S

    d. 5cm N + 7cm W +9cm S

    My answers:


    I want to know if a,b, and c are right; I dont know d.
  2. jcsd
  3. Dec 1, 2007 #2


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    Well, b and c are correct...I dont know what is a) and for part d) consider the N and S alone, and the "add'' to the W
  4. Dec 1, 2007 #3

    James R

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    Remember that a vector always has both magnitude and direction, so the answer to any vector addition is a vector. An answer that gives only the magnitude is incorrect, unless only the magnitude is asked for.

    (a) seems to have something missing, so we can't do that one.

    For (b), we have 5m S = -5m N so the sum is

    -5m N + 0.08m N = -4.92m N = 4.92m S

    For (c) we need to add things as vectors. This gives a resultant vector with magnitude

    [tex]\sqrt{30^2 + 50^2) = 58.3[/tex]

    The relevant angle from the south direction is

    [tex]\tan^{-1}(\frac{30}{50}) = 31^\circ[/tex]

    So the full answer is

    [tex]58.3\text{~m/s S~}31^\circ\text{W}[/tex]
  5. Dec 1, 2007 #4
    How did you get b?
  6. Dec 2, 2007 #5


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    A vector x in the south direction is equivalent to a vector -x in the north direction.
  7. Dec 2, 2007 #6
    a= 2cm N + 7cm W
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