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Uniform acceleration!~

  1. Apr 22, 2007 #1
    1. The problem statement, all variables and given/known data

    Time(s)| Distance(cm) from start
    0 | 0
    0.1 | 0.6
    0.2 | 2.4
    0.3 | 5.4
    0.4 | 9.6
    0.5 | 15
    0.6 | 21.6
    0.7 | 29.4
    0.8 |38.4
    0.9 |48.6
    1 | 60
    1.1 |72.6
    1.2 |86.4
    1.3 | 101.4
    1.4 |117.6
    1.5 |135


    thats the table...and i have to calculate the average speed during each time interval..


    2. Relevant equations
    vav= delta d/delta t ?


    3. The attempt at a solution

    well i kno to find the average speed i'd divide the distance/time...because vav=delta d/delta t...so am i right? if im wrong please correct me:rolleyes:
     
    Last edited: Apr 22, 2007
  2. jcsd
  3. Apr 22, 2007 #2

    Doc Al

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    Staff: Mentor

    Sounds good to me.
     
  4. Apr 22, 2007 #3

    Astronuc

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    Staff: Mentor

    The average speed is simply the distance traveled divided by the time over which the distance is traversed.

    or average V = ((x(n) - x(n-1))/(t(n) - t(n-1)). The instantaneous velocity (speed) is determined as the period (time interval) shrinks to a very small magnitude to determine V(t) = dx/dt.
     
  5. Apr 22, 2007 #4
    yeah but then on question number 3... it says.. the values you calculaed are the average speeds for the time interval, not the speed of the interval. To be more percise, the average speed is the speed at the midpoint of each time interval, and should be plotted there instead of at the end of each time interval. record the mid-interval times in your table...so if i just do average speed im alright? or do ihave to do the interval time?
     
  6. Apr 22, 2007 #5
    yeah but then on question number 3... it says.. the values you calculaed are the average speeds for the time interval, not the speed of the interval. To be more percise, the average speed is the speed at the midpoint of each time interval, and should be plotted there instead of at the end of each time interval. record the mid-interval times in your table...so if i just do average speed im alright? or do ihave to do the interval time?:surprised
     
  7. Apr 22, 2007 #6

    Doc Al

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    Staff: Mentor

    What you have been asked to calculate is the average speed during each interval. But, since instantaneous speed is not constant during the interval, as an approximation to the actual (instantaneous) speed at any given time you should associate that average speed to the midpoint of the interval--not to the beginning (or end) of the interval. Make sense?
     
  8. Apr 22, 2007 #7
    but i do average speed first still right??im confsued about the midpoint interval :confused:
     
  9. Apr 22, 2007 #8

    Doc Al

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    Staff: Mentor

    You started this thread by asking if your method for calculating the average speed in each interval was correct; it was.

    What's the actual problem you are trying to solve? Can I assume that this is data collected for some uniformly accelerating object? And that you need to figure out the acceleration? If so, there are many ways to go about it. Which way does your instructor want you to use?

    Plotting a speed vs. time curve is perfectly OK. (What kind of curve would you expect?) But the time you need to use for each interval is the time of the midpoint of the interval, since you are using average speed during the interval.
     
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