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Avg Velocity

  1. Sep 2, 2011 #1
    1. The problem statement, all variables and given/known data


    What is the average velocity of a runner whose 400 meter lap times are 60, 75, 65 and 60 seconds over a 1500 meter race?


    2. Relevant equations



    3. The attempt at a solution

    Is I use v=d/t (would the displacement be 0m beacuse he completed 1 lap?

    Im a bit confused will I need to average out the 4 times? then divide by 1500m?
     
  2. jcsd
  3. Sep 2, 2011 #2

    Hootenanny

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    This question is horrendously worded. If the runner completed four laps of a 400m track, then he would have traveled 1600m, not 1500m. I'm not sure if the last timing refers to the final 300m, or implied that the runner continued for an additional 100m after the race had finished. If it is the former, then the question can be answered (even though it is badly defined). If it is the latter, then the question cannot be answered.

    Could you seek clarification from your teacher?
     
  4. Sep 2, 2011 #3
    sorry, yes that is the questions I understood it as each 400m lap he psoted those times... therefore will I need to average out the 4 times and work out the average velocity over a 1500m race?? So confused...
     
  5. Sep 2, 2011 #4

    Hootenanny

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    If those times are indeed the 400m lap-times, then the question cannot be answered, in my opinion.
     
  6. Sep 2, 2011 #5
    I agree... but apprently the answer is 0m/s...
     
  7. Sep 2, 2011 #6

    Hootenanny

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    Over a 1600m race, that could be the case. However, over a 1500m race on a 400m track, that cannot possibly be the case. There is no way that a runner can start and finish a 1500m race at the same point on a 400m track.
     
  8. Sep 2, 2011 #7

    tiny-tim

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    Hey guys!

    Read the question!

    average velocity, not average speed!! :rolleyes:
     
  9. Sep 2, 2011 #8
    yes but avg velocity = change n dispalcement over chnage in time...

    so his displacemnt = 0 ... but his chnage in time?
     
  10. Sep 2, 2011 #9
    yes but avg velocity = change n dispalcement over chnage in time...

    so his displacemnt = 0 ... but his chnage in time?
     
  11. Sep 2, 2011 #10

    Hootenanny

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    Hi tt,

    I did read the question. However, if the runner is running on a 400m track, there is no way he can start and finish a 1500m race at the same point in space.
     
  12. Sep 2, 2011 #11

    tiny-tim

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    hi bionut! :smile:
    if his change in https://www.physicsforums.com/library.php?do=view_item&itemid=378" is 0, then the change in time doesn't matter, does it? :wink:
    Hi Hoot! :smile:

    Well, the answer is 0 m/s, so he must have done it somehow! :biggrin:
     
    Last edited by a moderator: Apr 26, 2017
  13. Sep 2, 2011 #12

    Hootenanny

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    Grrr.... I hate idiot teachers who sent idiotic questions. :grumpy:
     
  14. Sep 2, 2011 #13

    Doc Al

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    Could a typo be the culprit? Could that be a 1600 meter race? (How do you get four 400 m laps to add to 1500 m?)
     
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