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melmel Group Title

solve the pink one

  • one year ago
  • one year ago

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  1. melmel Group Title
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    • one year ago
  2. mathmate Group Title
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    Blue: Denote tension in cord as T. Vertical reaction on bar equals weight of bar, assuming no friction anywhere. Take moments about B. Solve for T.

    • one year ago
  3. melmel Group Title
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    how?

    • one year ago
  4. melmel Group Title
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    can you show to me

    • one year ago
  5. mathmate Group Title
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    "How" meaning to take moments?

    • one year ago
  6. melmel Group Title
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    yes but i'm confuse >.<

    • one year ago
  7. melmel Group Title
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    roller gve vertical force to the wall so therefore

    • one year ago
  8. melmel Group Title
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    |dw:1375615728179:dw|

    • one year ago
  9. melmel Group Title
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    |dw:1375615816627:dw|

    • one year ago
  10. melmel Group Title
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    also

    • one year ago
  11. mathmate Group Title
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    I can give an example: |dw:1375616654183:dw| A ladder 5 m long leans agains a smooth wall at B and stands on a rough floor at A at a distance of 3 m from the wall as shown above. The mass of the ladder is 10 kg. Since we don't know the friction on the floor, we can take moments about A so the friction does not come in the equation. Let reaction at B = R Mass at the middle (C) = m Take moments about A, since the ladder is in equilibrium, sum of moments = 0. -R*4 + mg*(3/2)=0 Note: moment = force * distance, clockwise is positive. Solve for R: R=(3mg/2)/4, or =3mg/8 N.

    • one year ago
  12. mathmate Group Title
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    |dw:1375617070605:dw|

    • one year ago
  13. melmel Group Title
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    yes u are right

    • one year ago
  14. mathmate Group Title
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    So you're good for both problems?

    • one year ago
  15. melmel Group Title
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    no

    • one year ago
  16. melmel Group Title
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    lets continue master

    • one year ago
  17. melmel Group Title
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    |dw:1375616151580:dw|

    • one year ago
  18. mathmate Group Title
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    Keep going, you're on the right track. I have an appointment, so have a little time left.

    • one year ago
  19. mathmate Group Title
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    Yes, what about the diagram?

    • one year ago
  20. melmel Group Title
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    what diagram?

    • one year ago
  21. mathmate Group Title
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    In the case of the ladder, there is a horizontal frictional force, F.|dw:1375617403359:dw|

    • one year ago
  22. mathmate Group Title
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    But taking moments at A will ignore that.

    • one year ago
  23. melmel Group Title
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    the roller does not give horizontal force master this will give only a horizontal force if the roller

    • one year ago
  24. melmel Group Title
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    is parallel to the wall

    • one year ago
  25. melmel Group Title
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    |dw:1375616451865:dw|

    • one year ago
  26. mathmate Group Title
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    |dw:1375617764714:dw| Would that help?

    • one year ago
  27. melmel Group Title
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    yes u are correct tension is there now can you teach me to take moment

    • one year ago
  28. melmel Group Title
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    where can i put my moment

    • one year ago
  29. melmel Group Title
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    basically i dont know where can i put the moment >.<

    • one year ago
  30. mathmate Group Title
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    |dw:1375617910870:dw| Moments tend to turn the object (bar) that you have isolated as a "free-body". Moment means the product of a force times the distance about a point. The distance must be the perpendicular distance, i.e. the shortest possible distance between the point and the direction of the force. Moments that turn the (free) body in a clockwise direction is positive, anti-clockwise is negative. So far so good?

    • one year ago
  31. melmel Group Title
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    yes i want to use the moment clock wise

    • one year ago
  32. melmel Group Title
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    so therefore?

    • one year ago
  33. mathmate Group Title
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    When you take moments about a point (say B), we assume that B does not move but free to turn. When the (free) body is in equilibrium, the sum of moments about any point is zero. So take moments about B: Ra*(3sin(60) - T(2cos(60)) = 0 Since Rb passes through point B, the distance is zero, so the product (moment) is also zero. Now you can solve for T in terms of Ra. (You know from the sum of forces in the vertical direction that Ra=mg).

    • one year ago
  34. melmel Group Title
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    yes i familiar that Ra=mg

    • one year ago
  35. mathmate Group Title
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    Are you able to solve for T now? By the way, in the future you would get more attention posting mechanics problems under Physics or Engineering. I enjoy solving mechanics problems.

    • one year ago
  36. melmel Group Title
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    wow

    • one year ago
  37. melmel Group Title
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    i become your fan :)

    • one year ago
  38. melmel Group Title
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    T=1273.06 ?

    • one year ago
  39. melmel Group Title
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    so im right?

    • one year ago
  40. mathmate Group Title
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    Yep, that's what I got (1274.356). You can solve the blue problem the same way. In any case, I've got to go. If you need more help, you may want to post the question again under physics or engineering, whichever you're onto.

    • one year ago
  41. melmel Group Title
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    thats all for the blue one?

    • one year ago
  42. melmel Group Title
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    i need also to solve the red one >.< dont go :)

    • one year ago
  43. mathmate Group Title
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    By the way, the minor difference is because I use g=9.81, when most people use 9.8. Yes, that's all for the blue one. Sorry, I meant you can solve the red one the same way.

    • one year ago
  44. mathmate Group Title
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    Can you draw the FBD for the red one?

    • one year ago
  45. melmel Group Title
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    yes

    • one year ago
  46. melmel Group Title
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    |dw:1375618026746:dw|

    • one year ago
  47. melmel Group Title
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    let me put the Rb and Ra and correct me if im wrong

    • one year ago
  48. melmel Group Title
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    |dw:1375618200791:dw|

    • one year ago
  49. mathmate Group Title
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    Here you know (again) that T=W=mg. |dw:1375619330484:dw|

    • one year ago
  50. mathmate Group Title
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    and that Ra=Rb by equilbrium of horizontal and vertical forces, right?

    • one year ago
  51. melmel Group Title
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    where did tou get 10 and 5 the distance of the assume box is 12m

    • one year ago
  52. melmel Group Title
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    i think yes their are equal but im not sure

    • one year ago
  53. mathmate Group Title
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    Oh, I was sloppy. It should have been 4 and 8 to make 12. The answer would have been the same. (you don't need to know that! :)

    • one year ago
  54. melmel Group Title
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    |dw:1375618365908:dw|

    • one year ago