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Homework Help: Big question on vectors!

  1. Dec 3, 2007 #1
    I need help with adding vectors. I basically want to know when do I use the pythagorean method and when do I simply add them.


    This has me confused.
  2. jcsd
  3. Dec 3, 2007 #2
    please. :(
  4. Dec 3, 2007 #3
    (1,1,1) + (1,1,1) = (2,2,2)

    magnitude of the vector is equal to

    square root of 2^2 + 2^2 + 2^2 = root pf 12
  5. Dec 3, 2007 #4

    I mean if its 8m N + 6 M E [example]

    should I do the theorem or no?
  6. Dec 3, 2007 #5


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    Draw a diagram. You will see that those vectors form two sides of a right angled triangle, of which the hypotenuse is the resultant.
  7. Dec 3, 2007 #6
    so if they are on a different axis: phythagorean thereom?
    same axis: add?
  8. Dec 3, 2007 #7
    if they are collinear then add them otherwise if the vectors are perpendicular (ie - 1 is North and the other is East) then you use the pythagorean thereom to find the resultant
  9. Dec 3, 2007 #8


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    To get the magnitudes then, yes, if two vectors point in the same direction you can add them to get the resultant. If not, it is always safer to draw a diagram.

    Note that, however, if you want to simply add vectors, you can do it component-wise; so if a=(x,y), b=(u,v), then a+b=(x+u,y+v).
  10. Dec 3, 2007 #9


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    If the angle between them is 0 or 180, you add or subtract as necessary...if the angle is 90 degrees...the hypotenuse is the resultant

    if the angle is any other obtuse angle...you use the parallelogram law
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