By how much is each post compressed?

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Homework Help Overview

The problem involves calculating the compression of wooden posts supporting a large aquarium, with specific dimensions and material properties provided. The context is within the subject area of mechanics and material properties, particularly focusing on the application of Young's modulus.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the calculations related to the compression of the posts, questioning whether the expected units for the answer might be a factor in the perceived incorrectness of the initial solution. There is also consideration of the type of water in the aquarium as a potential variable affecting the calculations.

Discussion Status

The discussion has evolved with participants exploring different aspects of the problem, including unit specifications and the implications of using salt-water versus fresh-water density. A participant has identified that the issue was related to significant figures, leading to a resolution of their initial confusion.

Contextual Notes

Participants note that previous questions had different requirements for significant figures, which may have contributed to the misunderstanding in this instance. There is an acknowledgment of the constraints imposed by the homework platform regarding the number of attempts allowed.

Wimpalot
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Homework Statement


A large 30000 L aquarium is supported by four wood posts at the corners. Each post has a square 6.00 cm x 6.00 cm cross section and is 90.0 cm tall. Take Y=10^10 for wood

Homework Equations


ΔL = FL/AY
F = ma
ρ = m/V

The Attempt at a Solution


So the total area is 0.06 * 0.06 * 4 = 0.0144m2
The length of each post is 0.9m
The total mass of water is 30000kg (taking the density as 1kg/L)
Meaning the weight is 30000*9.8 = 294000N
And Y=1010

Which gives:
ΔL = (294000*0.9)/(0.0144*1010
= 0.00184

But this is apparently wrong. I have no idea what I did wrong
 
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Were they expecting the answer to be given in particular units?
 
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It has never mattered before as I can specify the units. So it shouldn't matter.
 
Wimpalot said:
It has never mattered before as I can specify the units. So it shouldn't matter.
Well, I can't spot any other issues. Your calculations look okay to me. Unless of course this is a salt-water aquarium?
 
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gneill said:
Well, I can't spot any other issues. Your calculations look okay to me. Unless of course this is a salt-water aquarium?
That was my second thought. In which case I get 0.0019 which was also incorrect. So yeah, no idea what the issue is maybe they do want different units so I may try that otherwise I don't know. I only get 5 attempts (this is mastering physics)
 
Turns out every other question wants two significant figures except this one which wanted exactly 3 to be correct so yeah. 0.00184 was correct. Thanks for the assistance
 

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