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Homework Help: Need help on a rotational dynamics problem for tomorow please

  1. Dec 16, 2004 #1
    hi i need help understanding what to do with the information that was given in the problem if u could point mein the right direction i would greatly appreciate it. thank you

    An invered "A" is suspended from the ceiling by 2 verticle ropes. Each leg of the "A" has a length of 2L and a weight of 120.0N. The horizontal crossbar has a negligable weight. Find the force that the crossbar applies to each leg.
    W=120.0N per leg
    l of legs= 2L
    angle at top of "A" = 60Degrees
    l of crossbar=L
  2. jcsd
  3. Dec 16, 2004 #2


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    You have to figure out where the cross bar is located along the long legs.

    So draw a diagram of the inverted A. The angle at the bottom is 60°. Placing the crossbrace (length L) inside the A, it must make 60° with each leg then (and each side of the triangle formed is L. So the crossbrace attaches to the long leg at L (midway).

    But at the ends of the A, there is a tensile force (120 N) acting vertically on the leg. You then need to resolve the moment about the point of the A. This moment is acting on the crossbrace.

    Ratio of moment arms.
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