Static equilibrium with Youn modulus

AI Thread Summary
The discussion revolves around calculating the forces exerted by two steel wires supporting a 103 kg log in static equilibrium. The Young's modulus formula is highlighted as essential for determining the tension in each wire, considering their initial lengths and the log's horizontal position. It is noted that wire A is initially shorter than wire B, which affects the calculations for their respective strains and tensions. The relationship between the forces in the wires and the weight of the log is emphasized as critical for solving the problem. Understanding these relationships will lead to the final calculations for the forces in wires A and B.
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Homework Statement


In Figure, a 103 kg uniform log hangs by two steel wires, A and B, both of radiuses 1.20 mm. Initially, wire A was 2.50 m long and 2.00 mm shorter than wire B. The log is now horizontal. What are the magnitudes of the forces on it from Wire A, and Wire B?
Ysteel= 2.00*10^(11) Pa[url=http://www.freeimagehosting.net/rsgtl][PLAIN]http://www.freeimagehosting.net/t/rsgtl.jpg[/url][/PLAIN]

Homework Equations



Young Modulus = (F(perpendicular)/Area)/(ΔL/L(initial))

The Attempt at a Solution


This is static equilibrium
so

Summation of Forces:
F: Ta-Tb-Wb =0

Not sure where to take it from here. Can somebody give me a direction?

Homework Statement


Homework Equations


The Attempt at a Solution

 
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For a wire under tension, what is the formula for the amount it stretches?
 
SteamKing said:
For a wire under tension, what is the formula for the amount it stretches?

Would it be tensile strain?

Tensile strain=ΔL/L
 
Yeah, but what is the formula for calculating delta L?
 
SteamKing said:
Yeah, but what is the formula for calculating delta L?

Lfinal minus Linitial right
 
Read your problem carefully. You have two wires, one of which is slightly shorter than the other when there is no load (no tension) applied. After the log is suspended, it is perfectly horizontal, suggesting that both wires under tension are now the same length. How would you use the equation for Young's Modulus to calculate the tension in each wire?
 
If wire A had a length of L0A = 2.5 meters before it was loaded, and wire A had a length 2 mm shorter than wire B before it was loaded, what was the length L0B of wire B before it was loaded?

If FA is the force in wire A, and FB is the force in wire B, what is the equation for the strain εA and εB in each of these wires in terms of Young's modulus?

From this, and knowing the unloaded lengths of the two wires, write an equation for the loaded lengths of the two wires LA and LB. Since the log is horizontal, what does this tell you about the relationship between LA and LB? This should give you a single relationship between FA and FB.

How are FA and FB related to the weight of the log? This should give you your second relationship between the unknowns FA and FB.
 
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