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Homework Help: Please help! phys 2D motion

  1. Sep 19, 2005 #1
    At t = 0, a particle moving in the xy plane with constant acceleration has a velocity of vi = (3.00 i - 2.00 j) m/s and is at the origin. At t = 2.20 s, the particle's velocity is v = (9.20 i + 6.10 j) m/s.

    i am asked to find the acceleration at time t.
    i know that the acceleration is the derivative of the velocity, meaning the change in velocity divided by the time. so i took the difference between the vectors (v - vi) and got (6.2i + 8.1j)/(2.20 - 0). But i don't think it is expressed correctly in vectors. any help would be appreciate. thanks.
  2. jcsd
  3. Sep 19, 2005 #2
  4. Sep 19, 2005 #3

    I think you're on the right track, but it looks like you're trying to use time as a vector here. remember, it divides both components of your [tex]\Delta v[/tex] vector.
  5. Sep 19, 2005 #4


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    Well the first part, 6.2i + 8.1j is correct. You divide by 2.20 seconds but it looks more like (6.2/2.20)i + (6.10/2.20)j with m/s^2 being the units for the vector. You can treat them seperately and think of it like 6.2/2.20 as the dv/dt in the i direction for example.
  6. Sep 19, 2005 #5
    The vector representing acceleration would then be (6.2/t)i + (8.1/t)j ?
  7. Sep 19, 2005 #6
    That sounds right.
  8. Sep 19, 2005 #7
    thanks !!
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