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Drawing v-t and a-t from x-t

  1. Oct 12, 2015 #1
    I'm suppose to draw a v-t and a-t graph from a given x-t graph.

    Here is the x-t graph and my attemps on the other two graphs from the x-t one.

    1yMmwKP.png
    WyrQK4w.png

    DjswDiG.png

    Howeverr

    1. My teacher said that these graphs are discontinuous? Because I often see in littetaure that they drag "a vertical line" whenever something takes a jump, but it is discontinuous in the v-t graph right?

    2. If it is discontinuous, and no vertical line down, If i was given the v-t graph and wanted to do a x-t rgaph. Then I would "imagine" a vertical line right? To calculate an area ?

    3. Are these 2 graphs correct or what could be improved/ Whats wrong?
     
  2. jcsd
  3. Oct 12, 2015 #2
    Tbh it's rather poorly drawn, so my answer may be off.
    The position time graph appears to be a piecewise function. However, if it is mentioned in the question that it is continuous, then by default the graphs of all its derivatives (velocity-time and acceleration-time) should be continuous, so you must draw those "jump" lines.
    If the last section of the x-t graph is parabolic, then the other graphs are correct.
     
  4. Oct 12, 2015 #3

    BvU

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    Pretty crude pictures. If I look at the lower two, I wonder how v can change from something to zero with a staying at zero...
     
  5. Oct 12, 2015 #4

    BvU

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    I'd like to contradict this. A continuous function doesn't have to be continuously differentiable...
     
  6. Oct 12, 2015 #5
    That is true in general, but I have yet to see a position time graph that has an undefined gradient.
    EDIT: Unless you include some of those "jumps".
     
  7. Oct 12, 2015 #6
    ???? I dont understand what any of u talking is about. will their be a vertical line down on v-t graph or is there "space" between?

    this is not a queestion from a book, and u understand when i draw, Its just the "principle" not exact. Do i think right?
     
  8. Oct 12, 2015 #7
    Simply put - did the question say anything at all about the continuity of the x-t graph?
     
  9. Oct 12, 2015 #8

    BvU

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    Ok, fair enough. let's restart:

    1. The problem statement, all variables and given/known data

    from a given x-t graph, draw a v-t and a-t graph (top pic in post #1)
    given x(t) graph does not look like top pic ? could you post it, or describe the relevant details a little better ?
    2. Relevant equations

    ????​

    3. The attempt at a solution

    Lower two pictures in post #1
    main barrier: continuity or not ? for x? for v ? for a ?
    - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - -

    What is, according to what you have learned, the relationship between x(t) and v(t) ?

    and then we'll take it from there.


    --
     
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