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Homework Help: I Wanna Know

  1. Oct 6, 2004 #1
    how to do this problem:
    Let vector V = 36 i + 24 j - 57 k. What angles does this vector make with the x, y, and z axes?

    TY
     
  2. jcsd
  3. Oct 6, 2004 #2

    Gokul43201

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    What do you think ? Any ideas ?
     
  4. Oct 6, 2004 #3

    arildno

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    Do you know what the dot product (scalar product) is?
     
  5. Oct 6, 2004 #4
    Yea, I know what they are...but aren't they for when you have 2 vectors?
     
  6. Oct 6, 2004 #5

    arildno

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    What makes you think you haven't two vectors at your disposal?
     
  7. Oct 6, 2004 #6
    Can you expand on it more? The problem only gave me one.
     
  8. Oct 6, 2004 #7

    arildno

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    Well, does there exist, for example, a vector which is parallell to the x-axis, so that you could use this in calculating angle between the given vector and the x-axis?
     
  9. Oct 7, 2004 #8
    Could you show me an example? (maybe find the angle a 3-d vector (doesnt have to be mine) makes with the x-axis?)
     
  10. Oct 7, 2004 #9

    arildno

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    What's "i" in your equation?
    What does this symbol stand for?
     
  11. Oct 7, 2004 #10
    i is the x-component, j is the y-com, and k is the z-com.
     
  12. Oct 7, 2004 #11
    how about the X axis?
     
  13. Oct 7, 2004 #12

    arildno

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    Your vector is:
    [tex]\vec{V}=36\vec{i}+24\vec{j}-57\vec{k}[/tex]
    [tex]\vec{i}[/tex] is a unit vector PARALLELL to the x-axis, the number multiplied with it is the vector's component along the x-axis (that is, the vector's x-component).
    Another way of saying this, is that:
    [tex]\vec{V}\cdot\vec{i}=36[/tex]
    Are you now able to calculate the angle?
     
  14. Oct 7, 2004 #13
    I just began learning dot products, and I have never done such an operation like this...
     
  15. Oct 7, 2004 #14
    physicssss,
    i denotes a unit "vector" along x-axis
    j denotes a unit "vector" along y-axis
    k denotes a unit "vector" along z-axis

    if u find angle of x with i , then with j and then with k ....
    what will u have eventually?

    -- AI
     
  16. Oct 7, 2004 #15
    what is x in this case? I'm really confused...
     
  17. Oct 7, 2004 #16

    arildno

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    physicsssssss, TenaliRaman blundered, his sentence should read:
    "if u find angle of V with i , then with j and then with k ....
    what will u have eventually?"
    Does this clear up?
     
  18. Oct 7, 2004 #17
    not really...is there a formula for finding the angles a vector makes with the axes??
     
  19. Oct 7, 2004 #18

    arildno

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    But the i-vector lies along the x-axis!!
    So the angle between the vector V and the x-axis must be the same as the angle between i-vector and V
     
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