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Particle has position vector 2i + j

  1. Feb 20, 2005 #1
    A particle has position vector 2i + j (i is along x axis and j is along y axis) initially. and is moving with speed of 10m/s in the direction 3i-4j. Find its position vector when t=3 and the distance it has travlled in those 3 seconds.
    Please help me with the first part of the question. :confused:
     
  2. jcsd
  3. Feb 20, 2005 #2

    arildno

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    Your velocity vector must satisfy two conditions:
    1. It must be parallell to 3i-4j
    What does that tell you about the form of the velocity vector?
    2. The velocity vector's magnitude is 10.
     
  4. Feb 20, 2005 #3
    it says the particle is travelling in the direction 3i-4j, isnt that the velocity vector??
     
  5. Feb 20, 2005 #4

    arildno

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    Nope: the velocity vector is the time-derivative of the position vector.
    What you've been given is that the velocity vector is PARALLELL to (in the direction of) 3i-4j, that is:
    [tex]\vec{v}=k(3\vec{i}-4\vec{j})[/tex]
    where k>0 is a proportionality factor (unknown at the moment!).
    In addition, you have been given that the SPEED is 10, that is:
    [tex]||\vec{v}||=10[/tex]
    Use the last equation to determine k.
     
  6. Feb 20, 2005 #5
    phew...you just saved me from a headache. Now I get it. My value for k is 2.
     
  7. Feb 20, 2005 #6
    displacement is 20i -23j
     
  8. Feb 21, 2005 #7

    arildno

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    Yes, that's right.
     
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