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Question about this problem and Walter Lewin's video

  1. Mar 30, 2011 #1
    1. The problem statement, all variables and given/known data

    https://www.youtube.com/watch?v=4zb0t4H0Kec

    [​IMG]

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    The problem is EXACTLY the same.

    But one thing concerns me. The answer key said the force is [tex]-27\mu N \hat{i}[/tex]

    From Walter Lewin's method, I got [tex]+27\mu N \hat{i}[/tex]. Help?


    3. The attempt at a solution
     
  2. jcsd
  3. Mar 31, 2011 #2
    Is no one answering because no one is bothered to watch the video lol?
     
  4. Apr 5, 2011 #3
    Please...
     
  5. Apr 5, 2011 #4
    Flip the paper over. Then your i-hat will point the same way his does.
     
  6. Apr 5, 2011 #5

    SammyS

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    @Antiphon: Nice answer!

    @fp: He means left to right, not top to bottom.

    LOL
     
    Last edited: Apr 5, 2011
  7. Apr 5, 2011 #6

    SammyS

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    Seriously, Mr. Lewin clearly states that the force is toward the left.

    Therefore, it's in the [tex]-\hat{i}[/tex] direction.
     
  8. Apr 6, 2011 #7
    If you flip the paper over, how can you see your work?
     
  9. Apr 6, 2011 #8

    SammyS

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    Use thinner paper, write darker and/or use a light table.
     
  10. Apr 6, 2011 #9
    ...

    but what if I want to do it mathematically?
     
  11. Apr 6, 2011 #10

    SammyS

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    Did you see this?
     
  12. Apr 6, 2011 #11

    Andrew Mason

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    How do you get the force going to the right?

    AM
     
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