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Homework Help: One more Vector problem and we are good to go

  1. Sep 25, 2006 #1
    One more Vector problem and we are good to go!!!

    The Problem:
    Find the change in velocity of a yacht if it changes its velocity from
    5ms^-1 due north to 3ms^-1 due west and also state its direction.

    The solution :
    (resultant vel.)^2 = 5^2 + 3^2 = 5.8 ms^-1
    direction = tan-1(3/5) = 31 degrees west of north

    However , the books answer is 5.8 ms^-1 in a direction 31 degrees west of south . what am i doing wrong here ???
     
  2. jcsd
  3. Sep 25, 2006 #2

    radou

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    Draw down the vectors and it should become clear why the direction is 31 degrees west of south. Btw, the change equals [tex]\vec{v}_{2}-\vec{v}_{1}[/tex].

    http://upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Vector_subtraction.png/217px-Vector_subtraction.png" [Broken]
     
    Last edited by a moderator: May 2, 2017
  4. Sep 25, 2006 #3
    I did draw it but unless south means up and norths means down on paper I dont know what ur getting at lolz I wanna tear my book apart !!!!!!
     
  5. Sep 25, 2006 #4
    err .... got it !!! im so embarrased !!!

    thank you !!! :)
     
  6. Sep 25, 2006 #5

    radou

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    [tex]\vec{v}_{1}[/tex] is pointing north (up). [tex]\vec{v}_{2}[/tex] is pointing west (left). [tex]\vec{v}_{2}-\vec{v}_{1}[/tex] is then pointing south-west.
     
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