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brinethery

  • 4 years ago

Anyone good with vector problems involving moments?

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  1. brinethery
    • 4 years ago
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    Is my method correct or was I reading the problem wrong?

  2. brinethery
    • 4 years ago
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    http://www.scribd.com/doc/86313887/Problem-6

  3. eashmore
    • 4 years ago
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    I don't understand what they mean by "equally inclined to the positive ends of the orthogonal axis," but your methodology looks correct and complete.

  4. No-data
    • 4 years ago
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    You're totally wrong.... sorry

  5. No-data
    • 4 years ago
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    Just kidding. Your method is correct and you get the right answer. Congratulations.

  6. brinethery
    • 4 years ago
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    @eashmore my instructor writes all of these problems and this was the practice final exam. I think he wanted to make the questions as hard as possible. He wanted us to work backwards (r crossed with F = moment, so find the components of F). Equally inclined means this: You have an angle with the x-axis, with the y-axis and the z-axis. (Sorry if this info is nothing new to you!). A vector in 3-space has those 3 direction angles: alpha, beta, and gamma. If all angles are equally inclined, you can say: alpha=beta=gamma = theta (we'll just use theta so as not to cause confusion). If you square the cosine of each angle, that will equal 1. cos^2(alpha) +cos^2(beta) +cos^2(gamma) = 1 Since the angles equal eachother (equally inclined with the positive axes, we can say: cos^2(theta) +cos^2(theta) +cos^2(theta) = 1 3 cos^2(theta) =1 cos^2(theta) = 1/3 cos (theta) = 1/sqrt(3) Therefore, all alpha, beta, and gamma have direction cosines of 1/sqrt(3) So after all of that work, your unit vector will be: (1/sqrt(3))i +(1/sqrt(3))j +(1/sqrt(3))k Pg. 29 seems to explain this concept fairly well (see attached).

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  7. No-data
    • 4 years ago
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    I can give you harder problems if you want to practice.

  8. brinethery
    • 4 years ago
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    Well it was just the wording. Sometimes I have to read the question a few times to figure out what he wants.

  9. brinethery
    • 4 years ago
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    To be fair, some other people were on here last night and had no clue what was going on. Well I finished my final today and I'm all "vectored" out.

  10. No-data
    • 4 years ago
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    Yeah that equally inclined thing it's weird. Haha I bet you'll get a good grade.

  11. brinethery
    • 4 years ago
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    I will tell you what I don't get. The instructor gave 2 hours for the test. Some people finished in 50min, got up and left. Why not just sit around for the whole 2 hrs?

  12. No-data
    • 4 years ago
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    Well noboyd would notice them if they stay sit.

  13. No-data
    • 4 years ago
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    Or maybe they had to go to the bathroom =P

  14. brinethery
    • 4 years ago
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    HAHAHAHAHA I have something funny to mention

  15. brinethery
    • 4 years ago
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    I took multivar. calc last quarter and my teacher had us take the exams in the testing center. My classmate would sit in the testing center for like 5 hours taking her test. I asked her how she resisted going to the bathroom. She's like... I just hold it in.

  16. No-data
    • 4 years ago
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    Ohh poor girl! Five hours is insane!

  17. brinethery
    • 4 years ago
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    My instructor was really tough. The exams were all application-based and it had been 5 years since I'd been into math. My dad convinced me to sign up lol.

  18. No-data
    • 4 years ago
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    I wish you could help me with multivar calc. later

  19. No-data
    • 4 years ago
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    I don't quite understand. In which grade are you?

  20. brinethery
    • 4 years ago
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    I changed my mind about what field I want to go into.

  21. brinethery
    • 4 years ago
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    I took 3 quarters of calc starting when I was 17 and I'm 24 now.

  22. brinethery
    • 4 years ago
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    Which grade am I in? "Starting over!"

  23. No-data
    • 4 years ago
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    Sorry, but what were you studying before?

  24. brinethery
    • 4 years ago
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    to get into pharmacy school

  25. No-data
    • 4 years ago
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    Did you want to be a mathematiciand and then changed your mind?

  26. brinethery
    • 4 years ago
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    Nope, I am retarded at math compared to other people.

  27. No-data
    • 4 years ago
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    and now what is your major? Engineering?

  28. No-data
    • 4 years ago
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    I know you're not retarded but I can say is useful to think that haha.

  29. brinethery
    • 4 years ago
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    I think civil would be a good path. And hopefully I could get a job with county... anything having to do with infrastructure.

  30. No-data
    • 4 years ago
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    Ahh yeah! I remember you told me that long time ago!

  31. brinethery
    • 4 years ago
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    It's okay.

  32. No-data
    • 4 years ago
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    If I had to build a house I would call you =P

  33. brinethery
    • 4 years ago
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    It would crumble LOL!!!!!

  34. brinethery
    • 4 years ago
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    Hahaha "structurally unsound"

  35. No-data
    • 4 years ago
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    I'm so used to that now.

  36. No-data
    • 4 years ago
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    Do you study there ATM?

  37. No-data
    • 4 years ago
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    Please tell me when you get into statics. I have plenty of doubts on that!

  38. brinethery
    • 4 years ago
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    I'll brb... sec

  39. eashmore
    • 4 years ago
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    Thanks for the explaination of 'equally inclined.' @brinethery I've never heard that expression. Civil is a great field if you're interested in infrastructure. Everything from sky-scrapers to drainage ditches! Keep up the great work! You're problems are always challenging and then you end up solving them before I can!

  40. brinethery
    • 4 years ago
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    My teacher responded to my email this morning after I sent him the pdf file of what I wrote. He's like... no, no! Here's how you do it! Again, Jae saves the day :-)

  41. No-data
    • 4 years ago
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    what pdf?

  42. No-data
    • 4 years ago
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    Who is Jae?

  43. brinethery
    • 4 years ago
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    My instructor.

  44. No-data
    • 4 years ago
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    Was your problem wrong?

  45. brinethery
    • 4 years ago
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    You know the program Adobe that opens up those document files where you can only view them and do a tiny bit of editing? That's a pdf file.

  46. No-data
    • 4 years ago
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    hahaha I know what a pdf is =P

  47. brinethery
    • 4 years ago
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    The original problem was wrong. But then I uploaded the revision to Scribd. The link remains the same if it's a revision.

  48. No-data
    • 4 years ago
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    I meant what was the content of the pdf?

  49. No-data
    • 4 years ago
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    ahhh!

  50. brinethery
    • 4 years ago
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    I think I trashed the original, but it's wrong lol. But the current version is correct. I thought he was saying that F sub x and F sub y were equally inclined. But he corrected me on that.

  51. No-data
    • 4 years ago
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    That is great! I wish I had teachers like him =P

  52. No-data
    • 4 years ago
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    I had one but I failed miserably in his class. Shame on me.

  53. brinethery
    • 4 years ago
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    Actually he's teaching engr 106, but another instructor writes all of the exams and final exam. So that's probably why the exams are worded so strangely.

  54. No-data
    • 4 years ago
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    Thank you. I'd apreciated that!

  55. brinethery
    • 4 years ago
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    k, I'll create a link.

  56. No-data
    • 4 years ago
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    I want so bad to understand Maxwell's equations, but I suck at Calculus hehe

  57. No-data
    • 4 years ago
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    Perfecto!

  58. brinethery
    • 4 years ago
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    Sucks, I wish I had all the solns for at least one textbook. I don't think of it as cheating if I'm reading solutions as though I would read a textbook. It just helps to better understand things.

  59. No-data
    • 4 years ago
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    Maybe you're a different kind of learner.

  60. brinethery
    • 4 years ago
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    Sorry @eashmore we can bring the convo outside of here if you keep getting pop-up messages.

  61. eashmore
    • 4 years ago
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    Doesn't bother me. The wealth of notifications strokes my ego a bit. :-)

  62. brinethery
    • 4 years ago
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    Hahaha I'm totally abusing the system :-). I'll try to bring it away from here.

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