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Calculate instantaneous speed

  1. Mar 2, 2013 #1
    Gday mates,

    This is my question
    I uploaded a picture of the graph.
    Calculate the instantaneous speed when t=30 minutes, I have read something about limits but I don't understand and I am getting really frustrated. Please help ;)

    PS answer says 45 KLM/hour
     

    Attached Files:

  2. jcsd
  3. Mar 2, 2013 #2

    SteamKing

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    The instantaneous speed is the slope of the distance-time curve at t = 30 min
     
  4. Mar 2, 2013 #3
    That is what I thought... In that case the answer would be 75k/h
     
  5. Mar 2, 2013 #4

    haruspex

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    No, it's 45kph. Pls explain exactly how you are calculating the slope.
     
  6. Mar 3, 2013 #5
    By finding the gradient of the line the 30 mins corresponds to, it is rise 3 run 4. So gradient is equal to 3/4 or 75klm
     
  7. Mar 3, 2013 #6

    haruspex

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    What are the units of each step on the y axis; likewise on the x axis?
     
  8. Mar 3, 2013 #7
    Y axes is kilometers x axis is hours
     
  9. Mar 3, 2013 #8
    No, x axis is minutes.
     
  10. Mar 3, 2013 #9
    Yea whoops
     
  11. Mar 3, 2013 #10

    haruspex

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    If the grid lines were km and hours then your 3/4 should have produced 0.75 km/h.
    In fact, they're 5km and 5min.
     
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