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charlie_luna
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Homework Statement
An 80 N traffic light is supported at the midpoint of a line between two poles that are 30 m apart. If the light sags a vertical distance of 1 m at the midpoint, what is the tension in the supporting line?
A 20 lb picture is hung from a nail so that the supporting cords make an angle of 60. what is the tension of each cord segment?
Here is the actual homework problem i have to solve: An 80 N picture is hung from a nail as indicated. Assume the zeros in the 80 N weight are significant. The angle between the cords in 78 degrees. What is the tension in the each cord?
Homework Equations
I am lost here.
The Attempt at a Solution
And lost here.
There are 2 examples in my instructor's lecture notes that he sends to us by mail that has a street light and another picture hanging from 2 cords. in the street light problem, the tensions are all positive:
Tax = TaCosdegree
Tay = TaSindegree
Tbx = TbCosdegree
Tby = TbSindegree
and so on. But in the picture problem, some of the equations have a negative out front. such as:
Tbx = TbCos60
Tby = TbSin60
Tax = -TaCos60
Tay = TaSin60.
why is that? why would some problems be all positive and some get negatives in others? I have realized that i am suppose to set EFx = 0. where the E is the sigma symbol which i believe stands for equilibrium or net. and i am suppose to set EFy = 0.
can someone please help me understand this? my instructor has been out sick since last monday with swine flu and he has not returned to work yet.