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Instantaneous Velocity graph problem

  1. Jan 25, 2011 #1
    Find the instantaneous velocity at 1 s.
    Answer in units of m/s.

    the coordinate for 1s is (1,4)

    How do i find the instantaneous velocity?
  2. jcsd
  3. Jan 26, 2011 #2


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    welcome to pf!

    hi iiskenny! welcome to pf! :smile:
    by differentiating, or by drawing a tangent to the graph …

    but what's the rest of this function? :confused:
  4. Jan 26, 2011 #3
    Velocity is defined as the rate of change of position divided by the rate of change of time.

    This is the same as saying that velocity is the slope of the position vs. time graph.

    Therefore, instantaneous velocity at 1s is the slope of the position vs. time graph at t=1s.
  5. Jan 26, 2011 #4


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    But, as both tiny-tim and Beaker87 have said, just knowing the position is not enough! That's like saying "at 2:00, a car was at 4th st and Central ave. How fast was it going?"!

    You need to know something about it motion through that point. An actual "position function", telling where it was at different times, would be excellent- take the derivative of the function. If you are given a "x versus t" graph, you can estimate the slope of the tangent line at the given point. If you are given a position at another time, before or after this t= 1 you can estimate the speed at t= 1. If you are given the position at times before and after as well as at t= 1, you can get a better estimate.

    Now, what information are you really given? What is the full statement of the question?
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