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melmel Group Title

solve the pink one

  • 11 months ago
  • 11 months ago

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  1. melmel Group Title
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    • 11 months 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.

    • 11 months ago
  3. melmel Group Title
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    how?

    • 11 months ago
  4. melmel Group Title
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    can you show to me

    • 11 months ago
  5. mathmate Group Title
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    "How" meaning to take moments?

    • 11 months ago
  6. melmel Group Title
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    yes but i'm confuse >.<

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

    • 11 months ago
  8. melmel Group Title
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    |dw:1375615728179:dw|

    • 11 months ago
  9. melmel Group Title
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    |dw:1375615816627:dw|

    • 11 months ago
  10. melmel Group Title
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    also

    • 11 months 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.

    • 11 months ago
  12. mathmate Group Title
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    |dw:1375617070605:dw|

    • 11 months ago
  13. melmel Group Title
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    yes u are right

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

    • 11 months ago
  15. melmel Group Title
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    no

    • 11 months ago
  16. melmel Group Title
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    lets continue master

    • 11 months ago
  17. melmel Group Title
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    |dw:1375616151580:dw|

    • 11 months 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.

    • 11 months ago
  19. mathmate Group Title
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    Yes, what about the diagram?

    • 11 months ago
  20. melmel Group Title
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    what diagram?

    • 11 months 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|

    • 11 months ago
  22. mathmate Group Title
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    But taking moments at A will ignore that.

    • 11 months 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

    • 11 months ago
  24. melmel Group Title
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    is parallel to the wall

    • 11 months ago
  25. melmel Group Title
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    |dw:1375616451865:dw|

    • 11 months ago
  26. mathmate Group Title
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    |dw:1375617764714:dw| Would that help?

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

    • 11 months ago
  28. melmel Group Title
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    where can i put my moment

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

    • 11 months 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?

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

    • 11 months ago
  32. melmel Group Title
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    so therefore?

    • 11 months 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).

    • 11 months ago
  34. melmel Group Title
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    yes i familiar that Ra=mg

    • 11 months 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.

    • 11 months ago
  36. melmel Group Title
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    wow

    • 11 months ago
  37. melmel Group Title
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    i become your fan :)

    • 11 months ago
  38. melmel Group Title
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    T=1273.06 ?

    • 11 months ago
  39. melmel Group Title
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    so im right?

    • 11 months 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.

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

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

    • 11 months 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.

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

    • 11 months ago
  45. melmel Group Title
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    yes

    • 11 months ago
  46. melmel Group Title
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    |dw:1375618026746:dw|

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

    • 11 months ago
  48. melmel Group Title
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    |dw:1375618200791:dw|

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

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

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

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

    • 11 months 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! :)

    • 11 months ago
  54. melmel Group Title
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    |dw:1375618365908:dw|

    • 11 months ago