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Homework Help: Instantaneous Velocity with Position v. Time graph

  1. Sep 13, 2011 #1
    1. The problem statement, all variables and given/known data
    The position v. time graph for a certain object moving along the x-axis is shown.

    I don't have the graph. Bu I have the points.

    (0,-2), (1,9), (4,4), (6,4), (8,-4), (9,0)

    The object's initial position is -2m. Find the instantaneous velocity at .... (m/s)
    a.) 0.5s
    b.) 2.5s
    c.) 5 s
    d.) 8.5 s

    2. Relevant equations

    I think ....

    Instantaneous Velocity = (Xf - Xi) / (Tf - Ti)

    3. The attempt at a solution

    Well, I really don't understand where to start. Looking at the graph, for 0.5 sec ... I put 4. That was incorrect.

    I put in (4-(-2)) / (0.5 - 0) = 6/0.5 = 12. That's incorrect as well.

    I think I really don't understand the correct thing to do. If someone could give me some guidance or direction as how to tackle this I'd appreciate it. Thanks in advance!
  2. jcsd
  3. Sep 14, 2011 #2
    The first thing you need to do is realize for each ordered pair (a,b) which value is position and which is time?
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