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Average speed of a moving ball

  1. Oct 9, 2012 #1
    Hey guys so I'm stuck and only have a couple tries left meaning I've lost quite some marks on this question already and I can't risk anymore so the question is...

    A ball moves in a straight line (the x-axis). The graph in the figure (Figure 1) shows this ball's velocity as a function of time.
    http://tinyurl.com/8fkkvrs (graph)

    first question was: A) What are the ball's average velocity during the first 2.7 ?

    I got 2.3 m/s for this

    B) What are the ball's average speed during the first 2.7 ?

    2.3 m/s as well but the next two I don't understand what I have to do...


    C) Suppose that the ball moved in such a way that the graph segment after 2.0 was -3.0 instead of +3.0 . Find the ball's and average velocity during the first 2.7 in this case.

    D) Suppose that the ball moved in such a way that the graph segment after 2.0 was -3.0 instead of +3.0 . Find the ball's average speed during the first 2.7 in this case.
     
  2. jcsd
  3. Oct 9, 2012 #2

    tiny-tim

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    hi oldspice1212! :smile:

    speed is always positive (or zero): it's defined that way

    in a car, speed is what it says on the speedometer

    average speed is average reading of the speedometer​

    velocity can be negative (in 2D or 3D, of course, it can be in any direction)

    average velocity is total displacement over total time​

    show us your next tries at C) and D) before you submit them! :smile:
     
  4. Oct 9, 2012 #3
    For C I think it's (2+2-2.7)/3 to get the avg velocity which equals 0.43 but I got that wrong I'm not sure what i did wrong there.
     
  5. Oct 9, 2012 #4

    tiny-tim

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    it's not 2.7, and it's not 3 :redface:

    are you trying to do too much in your head (or misreading your own handwriting?)
     
  6. Oct 9, 2012 #5
    Err (2*2-3*0.7)/2.7?
     
  7. Oct 9, 2012 #6

    tiny-tim

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    yup! :smile:
     
  8. Oct 9, 2012 #7
    Sweet and for D) would it be (2*2+3*0.7)/2.7 = 2.259..2.3
     
  9. Oct 9, 2012 #8

    tiny-tim

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