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Finding average speed on a velocity vs time graph

  1. Dec 23, 2011 #1

    Again I find my self struggling on a question I had on a test, as my teacher is a "general studies" teacher, she is not much help with physics.

    the question is:

    What is the average speed of the car for the 10 second interval?

    I have uploaded the graph provided, if you can't see the graph. It is a standard velocity vs time graph. I have done some other searching on the internet, and what I have tried to do was:

    (v2+V1 / 2= vavg)t

    which did not bring me to the correct answer. I can do the math just fine, I am just not sure what formula I need to be using to find average speed on a velocity Vs. time graph.

    Thanks for the help

    Attached Files:

    • q51.bmp
      File size:
      128.9 KB
  2. jcsd
  3. Dec 23, 2011 #2
    The graph you enclose is ACCELERATION against time and is for 8secs not 10
  4. Dec 23, 2011 #3
    a yes.... so you see my frustration's with my course....
    I realize this graph does not match what is being asked, and since my teacher is on winter break I can not ask her why.

    My plan is to just use this graph (which was the one provided for the question) and just solve for the graph... not for the 10 second graph requested. My problem being is that finding speed on a acceleration graph has yet to be covered in the course. So I have no idea which equation to use.
  5. Dec 23, 2011 #4
    Tell her the question is impossible to solve because she fails to include the velocity at t = 0 and 2 seconds of the time interval she's requesting.
  6. Dec 24, 2011 #5
    Try to get something from it !!!!! If there is a mistake (I think there is !!) and this is a 'standard velocity - time graph' (which makes more sense) then the total distance travelled is the area under the graph which I get to be 16m.
    16m covered in 8secs means average speed of 2m/s.
    It is not the question as posed but it, at least, shows that you have some idea how to work out average speed.
    Don't do nothing !!!!!!
  7. Dec 24, 2011 #6


    User Avatar

    Staff: Mentor

    Hint: there's a difference between speed (what you're asked for) and velocity (which the graph shows). What is it?
  8. Dec 26, 2011 #7
    *raises hand*

    speed is the absolute value of the velocity!
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