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Tangent line to a particles path at a specific time?

  1. Sep 27, 2005 #1
    how do you find orientation of a line that is tangent to the particle's path at t = 2.10 s?(from the +x axis)
    before this i found the position r of a particle moving in an xy plane is given by r = (1.00t3 - 8.00t) i + (7.00 - 4.00t4) j.
    So I found r,v,a, for t=2.10s (all in m)
    r=-7.54 i +-70.8 j
    v=5.23 i + -148 j
    a=12.6 i + -212 j
    i first tried using v's i and j to make a triangle and find the angle from that by inverse tan (-148/5.23) and got -87degress or -212 but that was wrong...
    any help?
  2. jcsd
  3. Sep 27, 2005 #2
    i got 272 degree from the + x axis in anticlockwise direction.
  4. Sep 27, 2005 #3
    how did u get that?
    did you just do the inverse tan and adding to 360? does that make sense?
  5. Sep 27, 2005 #4
    your v lies in the fourth quadrant.
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