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Motion in 2 dimensions

  1. May 28, 2008 #1
    Hi,

    I have a Mechanics vector problem here split in two parts. First to solve the magnitude of the resultant vector and then to give the bearing at which it's acting at. Worked out most of it, but the last answer to the question isn't the same as mine. Kind of difficult to explain the question since I would need a diagram but hey, here it is:

    Question:

    A particle has velocity 4ms^-1 acting on it, in the east direction followed by a velocity of 5ms^1 acting at 30 degrees to the east direction.

    I found the resultant vector to be of magnitude 8.7 ms^-1, But a bearing of 73.3 degrees???

    The magnitude part is right however, they give a bearing of 20.5 degrees rather than 73.3.

    For my bearing I done: 90 - tan^-1(5sin30/(4+5cos30)).

    Any help? Thanks.
     
  2. jcsd
  3. May 28, 2008 #2

    Dick

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    "For my bearing I done" is atrocious grammar. For your bearing I did exactly the same thing you did. And I got 73.29468619399003 degrees. Check your calculator skills. The basic math seems fine.
     
  4. May 29, 2008 #3
    Atrocious grammar? How should it be corrected?

    Also, I don't understand how the textbook can give a wrong value of bearing 20.5 degrees when you've ended up with an identical answer to me of 73.3 degrees.

    I've checked my calculator skills, they seem pretty fine.
     
    Last edited: May 29, 2008
  5. May 29, 2008 #4

    Vid

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    It's simple subject-verb agreement. The error itself is inexcusable, but you not seeing it after it was pointed out to you is even worse.
     
  6. May 29, 2008 #5

    tiny-tim

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    wotcher essaichay! :smile:

    It's "For my bearing I done, guv!"

    And I make it 73.3 also … looks like the book answer is wrong. :frown:
     
  7. May 29, 2008 #6
    You know, you could've just replied with a simple correction to the question I asked on how to correct it. "I'm sorry" my grammar isn't the best, but at least you understand (I hope) what I'm saying, and right now, I'm completely confused.

    Another option was to actually answer the real query I had about the textbook giving a bearing that was wrong to my solution. And that, I would've been grateful for.
     
  8. May 29, 2008 #7
    lol. Thank you.
     
  9. May 29, 2008 #8

    HallsofIvy

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    Dick and Vid, the internet is world-wide. It's your good fortune that most of it is in a language that you speak fluently. For a lot of the people who post here, English is not their native tongue. Cut them a little slack. I'm sure they will be glad of your correcting their grammar, but not just saying it is wrong.

    Essaichay, "done" is the "past participle" of "do". It is always used with "have" or "had". What you wanted was "For my bearing I did ...". Unfortunately, "I done" is so common among English speakers who are just careless with grammar- and other things- I'm afraid it triggered an automatic reaction in Dick.
    (And both Dick and Vid did answer your original question.)
     
  10. May 29, 2008 #9

    tiny-tim

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    yeh … but no … but … http://en.wikipedia.org/wiki/She_Done_Him_Wrong
    :smile: … though, technically, IM'UO, it should be "She Done 'im Wrong"! :smile:
     
    Last edited: May 29, 2008
  11. May 29, 2008 #10

    Dick

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    The grammar thing was 'just kidding'. I actually carelessly thought that the book said 73.3 and you were getting 20.5. That's why I was suggesting you check how you calculated it. Sorry.
     
  12. May 29, 2008 #11
    OK! woah! STOOPPP everyone!

    CONCLUSION:

    -I should've written: did not done
    -The textbook has YET AGAIN given me a wrong answer.

    :biggrin: Thanks everyone.
     
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