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Average velocity question

  1. Sep 6, 2012 #1
    Here is my problem:

    A stone is tossed in the air from ground level with an initial velocity of 20m/s. Its height at time t is h(t) = 20t-4.9t^2 m. Compute the stones avg velocity over the time interval [1.5,2.5].

    I understand how to compute average velocity its Vavg=change in distance/change in time. However, I am running into a problem trying to figure a change in distance from the equation they gave me.

    I tried searching in the library for a similar question but could not find one.
     
  2. jcsd
  3. Sep 6, 2012 #2
    What is the height at time t = 2.5 s?
    What is the height at time t = 1.5 s?
    How much time elapsed between time t = 1.5 s and time 2.5 s?
     
  4. Sep 6, 2012 #3
    Oh I get it so I plug those values into the formula to get the height and then I compute the average velocity? Cool thanks!
     
  5. Sep 7, 2012 #4

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Important point- if you throw a rock from ground level so that it goes to a very great height, then comes down and hits the ground again, obviously it must have had a large velocity at certain time. But since it started at ground level and got back to ground level, its net distance traveled is 0 and its average velocity over that time is 0.
     
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