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Homework Help: Position versus Time graph

  1. Dec 17, 2012 #1
    1. The problem statement, all variables and given/known data
    A plot of Calvin's Mom's position vs. time is shown. Rank the acceleration of the five regions (e.g., A, B, etc.) from most negative to most positive

    See attachment!!!
    2. Relevant equations

    3. The attempt at a solution I think that b is the most negative and c is zero, a is increasing acceleration but I just dont understand how to read this graph. Please help my final is tomorrow!!! thanks

    Attached Files:

    • PvsT.gif
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  2. jcsd
  3. Dec 17, 2012 #2


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    This is position vs. time, so the derivative (slope at any point) of this graph gives the velocity.

    The rate of change of the velocity is the acceleration.

    So, on this graph:
    Where is the slope increasing?

    Where is the slope decreasing?

    Where is the slope constant?​
  4. Dec 17, 2012 #3
    well, the slope is increasing at a, and maybe at e, its constant at c, and decreasing at d, then at b it is slowing down
  5. Dec 17, 2012 #4


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    Is the slope (not the function itself) really decreasing in D?
    The other parts are right.
  6. Dec 17, 2012 #5
    well at first i thought d was constant and since slope relates to the velocity then a is zero but iam just really confused when trying to read this graph
  7. Dec 17, 2012 #6


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    Your first thought was right. D corresponds to a constant, negative velocity. No acceleration there.
  8. Dec 17, 2012 #7
    ok that makes sense, thanks!
  9. Jan 21, 2013 #8
    Bumping an old thread for a little help on a similar question.

    I am given a position vs time graph:

    I am asked where acceleration is positive and where it is negative.

    I believe I understand that when the slope of the line is increasing then the acceleration is positive. When the slope of the line is decreasing then the acceleration should be negative. Correct?

    So from what I see here acceleration at the given points should be:
    A - Negative
    B - 0
    C - Negative
    D - Positive
    E - 0
    F - Positive

    Yet these answers are being marked as incorrect when I submit them. Can PF lend me a hand here? Thank you!
  10. Jan 21, 2013 #9
    I think B and E are incorrect.

    Curvature upward acceleration is positive and curvature downward acceleration is negative.
  11. Jan 21, 2013 #10
    B and E appear to be where the object changes direction. An earlier part of the question asked where velocity was 0 and those were the correct answers. Can you have acceleration without velocity?
  12. Jan 21, 2013 #11
    Apparently you can, that was the correct answer, thank you!
  13. Jan 21, 2013 #12
    Well I thought that you were looking for acceleration.
  14. Jan 21, 2013 #13
    Yo if the graph is position vs time then velocity would be zero when the slope is zero but if they ask for acceleration then its different. (refer back to my original post).
  15. Jan 21, 2013 #14
    Re: Re: Position versus Time graph

    Yep, got it now. I guess I wasn't thinking of local min/max points as a change in slope. Not sure why... Ha. Thank you again!
  16. Jan 21, 2013 #15
    Yeah no problem! Can you help me on my post? :)
  17. Jan 21, 2013 #16


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    I see that you're new to PF, so Welcome!

    I should point out that according to the rules of this forum, you should have started a new thread to post this rather than "highjacking" an existing thread.
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