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Homework Help: Need help FAST

  1. Feb 14, 2008 #1
    An artist friend of yours needs help hanging a sculpture from the ceiling. For artistic reasons, she wants to use just two ropes. One will be from vertical, the other . She needs you to determine the smallest diameter rope that can safely support this expensive piece of art. On a visit to the hardware store you find that rope is sold in increments of diameter and that the safety rating is pounds per square inch of cross section. What size (diameter) rope should you buy?
    Give your answer to the nearest 1/8 inch.

    Fx= T2sin60 - T1sin(30)= 0
    Fy= (T1cos30 + T2cos60) -mg = 0

    T1= (T2sin60)/ sin30

    mg= ((T2sin60)/ sin30) cos30 + T2cos60

    mg = 1.5 T2 + .5T2
    mg = 2T2
    T2= mg/2 where T2 is the 60 degree
    T1= T2sin60/sin30

    If you change g=9.8 to 32
    T2= 500 * 32/2= 8000

    So pi(n/16)^2 * 4000 > or equal to T2
    so pi(n/16)^2 * 4000 > or equal to 8000
    pi(n/16)^2 > or equal to 2

    What do I do now to find the needed diameter?????
    PLEASE HELP!!!! I have to complete this by Tomorrow

    Last edited: Feb 14, 2008
  2. jcsd
  3. Feb 15, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Realize that you left out essential information when you presented the problem. For example, what's the strength rating of the rope?

    Once you find the tension in each rope, you just need to find the minimum (I presume) diameter of rope that would survive such tension. If the rope is rated at X lbs/in^2, find the cross-sectional area of rope needed. Then convert that area to a diameter: [itex]A = \pi r^2 = \pi (d/2)^2[/itex].
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