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Question about a 2 dimensional motion question

  1. Oct 11, 2007 #1
    1. The problem statement, all variables and given/known data

    At one instant a bicyclist is 35 m due east of a park's flagpole, going due south with a speed of 9 m/s. Then, 21 s later, the cyclist is 30 m due north of the flagpole, going due east with a speed of 15 m/s. For the cyclist in this 21 s interval, find each of the following.

    2. Relevant equations



    3. The attempt at a solution

    first of all, i don't even understand the question. it says 35m due east then it says due south with a speed of 9m/s. can anyone please clarify the problem for me
     
  2. jcsd
  3. Oct 11, 2007 #2

    learningphysics

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    That means his position is 35m east of the flagpole. But his velocity is 9m/s southbound...
     
  4. Oct 11, 2007 #3
    what does it mean by 9m/s south bound
     
  5. Oct 11, 2007 #4

    learningphysics

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    Means the direction he's travelling is south... downwards...
     
  6. Oct 11, 2007 #5
    yeah but the postion is east though, that's what doesn't make sense to me. so is it south east
     
  7. Oct 11, 2007 #6

    learningphysics

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    position and velocity are two separate things... a person can be located anywhere and still be travelling in the south direction... ie downwards... at that particular moment he's located east of the flagpole... in while after he's travelled south a little more he won't be directly east of the flagpole... he'll be south east...

    But at that particular moment he is east of the flagpole... and his instantaneous velocity is south...
     
  8. Oct 11, 2007 #7
    so he goes 35 m east and then 9 m/s south?
     
  9. Oct 11, 2007 #8

    learningphysics

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    No his location is 35m east of the flagpole... we don't know how he got there. he's travelling at a speed of 9m/s in the south-direction.

    Draw a picture. I think you're making it more complicated that it needs to be...
     
    Last edited: Oct 11, 2007
  10. Oct 11, 2007 #9
    ok i get the first part but how does he end up north of the flag pole later on
     
  11. Oct 11, 2007 #10

    learningphysics

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    we don't know... anything could have happened in those 21s... what does the question ask you to find?
     
  12. Oct 11, 2007 #11
    it asks for the average acceleration, velocity, and displacement and the magnitude and direction of each
     
  13. Oct 11, 2007 #12

    learningphysics

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    ok. try calculating them... start with displacement...
     
  14. Oct 11, 2007 #13
    so would this be the right picture and the redline is the displacement?
     

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  15. Oct 11, 2007 #14

    learningphysics

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    can't see the picture yet... might be a good idea to post on some image sharing site...

    you can try this one:

    http://www.imagevimage.com/
     
  16. Oct 11, 2007 #15
  17. Oct 11, 2007 #16

    learningphysics

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    that's not right. you're making it more complicated than it is... just start with displacement... ignore velocity for now...

    The initial position is 35m east of the flagpole. The final position is 30m north of the flagpole. What is the displacement?

    You should just have a line/arrow from the point 35m east of the flagpole, to the point 30m north of the flagpole.

    What is the magnitude of this line? What is the direction?
     
  18. Oct 11, 2007 #17
    i understand the problem. thanks.
     
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