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Homework Help: Kinematics in 2D

  1. Oct 12, 2007 #1
    1. The problem statement, all variables and given/known data
    A particle moves in the xy plane with constant acceleration. The particle is located at [tex]\vec{r} = 2\hat{i} + 4\hat{j}[/tex] m at t=0s. At t=3s it is at [tex]\vec{r} = 8\hat{i} - 2\hat{j}[/tex] m and has a velocity [tex]\vec{r} = 5\hat{i} - 5\hat{j}[/tex] m/s

    What is the particle's acceleration vector a?
    2. Relevant equations

    3. The attempt at a solution

    Here's what I did
    [tex]\vec{a} = (\hat{r_{1}} - \hat{r_{2}}) / \Delta t - \vec{r} = 5\hat{i} - 5\hat{j}[/tex]

    The answer is just that without the [tex]\vec{r} = 5\hat{i} - 5\hat{j}[/tex]

    Could someone tell me why?
  2. jcsd
  3. Oct 12, 2007 #2


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    Homework Helper

    wait what is the answer?
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