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Homework Help: Please help me : constant velocity.

  1. Jul 1, 2008 #1
    Hi guys, I'm reallyyyy stuck on this so I would really appreciate your help, cheers :)

    2. Particle P passes through posiion A (12,3) with constant velocity i + 2j m/s. At the same time Particle Q passes through position B (3,-3) with c.v 2.5i + 3j m/s. Find the position vectors of P and Q after time t seconds. Show that they collide. If the point of collision is X, find the time taken for P to travel from A to X. Find the position vector of X.

    3. It's just finding the position vector of X that I need help with...please?! :D
  2. jcsd
  3. Jul 1, 2008 #2

    Doc Al

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    Staff: Mentor

    What have you done so far?
  4. Jul 1, 2008 #3


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    Have you found the position vectors (as functions of t) for P and Q to begin with?
  5. Jul 3, 2008 #4

    Andrew Mason

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    i and j are the orthogonal unit vectors in the plane:

    [tex]\vec {v_P} = 1\hat i + 2\hat j \text{ m/sec}[/tex]


    [tex]\vec {v_Q} = 2.5\hat i + 3\hat j \text{ m/sec}[/tex]

    Write out the displacement of P from the origin as a function of time: [itex]d_P(x(t), y(t))[/itex] and do the same for Q.

    What is the relationship between the displacements (ie the coordinates) of P and Q at the time of a collision?

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