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Homework Help: Vectors and Magnitudes

  1. Sep 28, 2008 #1
    Hey guys, I am posting this question because I don't know what it is asking of me. Here it is:


    Any tips or help would be nice. Thanks.
  2. jcsd
  3. Sep 29, 2008 #2
    You probably have to detemine the i vector component of the astronaut's speed to hit the airlock.
  4. Sep 29, 2008 #3
    How do I go about doing that? The pictures confuses me.
  5. Sep 30, 2008 #4
    Sorry I got it wrong, you have to determine the part of the velocity verctor that is parraler to the verctor pointing from astronaut to the airlock. Which is [tex]|\overline{v}| cos \varphi[/tex]. Using [tex]|\overline{v}||\overline{u}|cos \varphi = |\overline{v}\cdot\overline{u}|[/tex] you should get it.
  6. Sep 30, 2008 #5
    OK thanks that makes sense. So would I Subtract Ra from Rg to get a vector and use the dot product with the velocity vector?
  7. Oct 1, 2008 #6
  8. Oct 1, 2008 #7
    What am I doing wrong here. Here is the steps I was doing.
    1. U = Rg - Ra = 72.2i + 100j + 154k

    2. U . V (dot product) = -880

    3. magnitude of V = 4.798. magnitude of U= 197.3

    4. -880/ (197.4 x 4.798) = -0.9296 = 158.374 degrees (using cos)

    5. magnitude of of V x Cos(158.374) = -4.46 <------ not correct

    Please help!
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