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Homework Help: Avg Velocity and Avg Speed

  1. Sep 27, 2005 #1

    badtwistoffate

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    doing this problem 400km East in .75 hrs from a to b and 960 km south in 1.5 hrs from b to c.
    Ang Velocity is /Delta x divided by /delta t correct?
    and avg speed is just adding the distance's and times and diving by the time right?
    Well for the avg velocity for this problem its saying its wrong any help?
     
    badtwistoffate, Sep 27, 2005
  2. jcsd
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  3. Sep 27, 2005 #2

    Doc Al

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    Staff: Mentor

    Show exactly what you did. To find the average velocity, start by finding the displacement.
     
    Doc Al, Sep 27, 2005
  4. Sep 27, 2005 #3

    badtwistoffate

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    found displacement by using a right-hand coordinate system. and did solved by doing a^2 + b^2 = c^2. got the displacement to be 1040 km for the total trip. (Checked it its right)
    Did velocity avg by 960-400/1.5-.75 = 747 and it says its wrong....
     
    badtwistoffate, Sep 27, 2005
  5. Sep 27, 2005 #4

    Doc Al

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    Staff: Mentor

    You found the correct displacement, now use it to find the average velocity.
    I have no idea what you are calculating here. What happened to the displacement that you just calculated? That's what you need to use.
     
    Doc Al, Sep 27, 2005
  6. Sep 27, 2005 #5

    badtwistoffate

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    well it said change in x over change in t
    960 and 400 was the two distances, how to apply the displacement? do i subtract from that?!
     
    badtwistoffate, Sep 27, 2005
  7. Sep 27, 2005 #6

    Doc Al

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    Staff: Mentor

    Average velocity is just displacement divided by time. Do it!
     
    Doc Al, Sep 27, 2005
  8. Sep 27, 2005 #7

    badtwistoffate

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    but what does my schaums outline says change in x over change in timee, im confused :(
    is it displacement over change in time or total time?

    also isnt displacement delta x?
     
    Last edited: Sep 27, 2005
    badtwistoffate, Sep 27, 2005
  9. Sep 27, 2005 #8

    Doc Al

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    Staff: Mentor

    Displacement is measured from origin to final position; so is the time. Average velocity = the total displacement divided by the total time. The "change" in time is from 0 to the final time.
     
    Doc Al, Sep 27, 2005
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