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Help with instantaneous velocity

  1. Sep 6, 2004 #1
    I was given the following graph:


    I must find the instantaneous velocity at T=1.4

    The formula for instantaneous velocity is delta x/delta t as t approaches zero. However, I'm still not sure how to work this problem. Please help
  2. jcsd
  3. Sep 6, 2004 #2
    Find the equation for x(t) in the interval t = [0,2]. You should know the velocity by then.
  4. Sep 6, 2004 #3


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    The formula you gave is for instantaneous acceleration, not velocity. So I will assume you are looking for instantaneous acceleration.
    You will note the graph is a straight line from 0 - 2 seconds which means the acceleration is constant. The instantaneous acceleration is therefore the same as the average acceleration over that interval.
  5. Sep 6, 2004 #4
    No, its instantaneous velocity that I'm looking for. I thought instantaneous acceleration is the change in velocity over the change in time.
  6. Sep 6, 2004 #5
    HOWEVER though, the graph does not show change in velocity over change in time. It's simply distance vs time. Besides, Ramin gave the right formula, distance over change in time. i think you should ignore chrono's comments Ramin......

    Since it is a straight line though, the velocity is not changing, so you can just find the instantaneous velocity by finding the slope of the 0-2 second interval(since t = 1.4 has the same velocity as that interval)
    Last edited: Sep 6, 2004
  7. Sep 6, 2004 #6


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    My bad, you are correct, dx/dt. Make a table x1, t1, x2, t2. x1 and t1 will always be 0,0. x2 and t2 will be per the graph. solve for dx/dt at t2 = 1.4 seconds. Hint dx is always x2 - x1 and dt is always t2 - t1
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