1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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.




    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


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    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


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    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


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    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.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted