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Homework Help: Cross product

  1. Apr 19, 2005 #1

    tony873004

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    find the cross product a x b of the vectors a = 5.0m,i and b=4.3m,k
    [tex]5.0m\ast 4.3m\ast \sin (90)=22m^2,\hat {j}[/tex]

    The back of the book gives
    [tex]-(22m^2)\hat {j}[/tex]

    Where does the minus sign come from?
     
  2. jcsd
  3. Apr 19, 2005 #2

    dextercioby

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    Naturally

    [tex] \vec{i}\times\vec{k}=-\vec{j} [/tex]

    ,because

    [tex]\vec{k}\times\vec{i}=\vec{j} [/tex]

    Daniel.
     
  4. Apr 19, 2005 #3

    tony873004

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    thanks, dextercioby
     
  5. Apr 19, 2005 #4

    HallsofIvy

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    Or: "right hand rule". Curl the fingers of your right hand from the positive x-axis (i) to the positive z-axis "j". You thumb will be pointing down the negative y-axis.
     
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