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Homework Help: Simple displacement and acceleration question

  1. Mar 4, 2013 #1
    1. The problem statement, all variables and given/known data

    Find the body's displacement and average velocity for the given time interval.

    s=t^2 -3t +2, 0<=t<=2

    2. Relevant equations

    d(displacement)/d(time) is for the acceleration right?

    3. The attempt at a solution

    So here is my problem. I got 2t-3 for the derivative, but i don't really know how to apply it to the question. I feel like i need just one value for t in order to find the displacement and velocity at that point, right? So how do i incorporate a full interval, 0 to 2? The back of the book says -2 for displacement and -1 for acceleration, but i have no clue how that is the case when you have multiple values of t. I would have just said the 2t-3.
  2. jcsd
  3. Mar 4, 2013 #2
    What does the given equation represent? Position? Velocity? Acceleration?

    The change in POSITION(not displacement, they are related but not the same) over the change in time is velocity. the change in velocity over the change in time is accleration.

    d(POSITION)/d(time) is not acceleration. When you get confused on these, try and just think about the units you would be working with it. X(meters) over T(seconds) That is m/s which is velocity.

    I think you are getting position and displacement confused. Position is simply where something is at any given time. Where as the displacement is Δx or the change in its position. Additionally, you are dealing with the CHANGE in time. That being said, yes. It is neccessary to have more than one value for t.
    Last edited: Mar 4, 2013
  4. Mar 4, 2013 #3

    Doc Al

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    Staff: Mentor

    There's no need for calculus here. You are given the position (s) as a function of time.

    What's the definition of displacement?

    What's the definition of average velocity? (They want velocity, not acceleration.)
  5. Mar 4, 2013 #4


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    Staff Emeritus
    Science Advisor
    Homework Helper

    What is s(t) when t = 0? What is s(t) when t = 2?
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