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Homework Help: What time t does the particle first cross the x axis?

  1. Sep 17, 2010 #1
    1.
    (a) A particle has ~r(0) = (4 m)j and ~v(0) =
    (2 m/s)i.
    If its acceleration is constant and given by
    ~a = −(2 m/s2) (i+j), at what time t does the
    particle first cross the x axis?
    Answer in units of s.

    (b) At what time t is the particle moving parallel to the y axis; that is, in the j direction
    Answer in units of s




    2.Some equation with a constant acceleration... not sure which one



    3. I tired to draw it out but I don't know how... I don't understand how to start the problem
     
  2. jcsd
  3. Sep 18, 2010 #2

    ehild

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    Homework Helper

    Do you know what those i and j are?

    ehild
     
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