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Homework Statement
[PLAIN]http://img714.imageshack.us/img714/7747/43416215.jpg
The attempt at a solution
I have already solved parts (a) and (b). It's part (c) that I can't get.
To get a minimum thickness at 50 MPa, I thought that the hoop stress equation would govern. Here is my calculation for it:
[tex]\sigma = \frac{Pr}{t}[/tex]
Solving for t, I get:
[tex]t = \frac{Pr}{\sigma}[/tex]
[tex]t = \frac{(1200*10^{3} Pa)(0.5m)}{50*10^{6} MPa}[/tex]
[tex]t = 0.012 m[/tex]
[tex]t = 12 mm[/tex]
However, this is not the answer. The answer takes the longitudinal stress equation as the governing one. Therefore, the solution is half of mine, a thickness of 6 mm.
Why is this so?
[PLAIN]http://img714.imageshack.us/img714/7747/43416215.jpg
The attempt at a solution
I have already solved parts (a) and (b). It's part (c) that I can't get.
To get a minimum thickness at 50 MPa, I thought that the hoop stress equation would govern. Here is my calculation for it:
[tex]\sigma = \frac{Pr}{t}[/tex]
Solving for t, I get:
[tex]t = \frac{Pr}{\sigma}[/tex]
[tex]t = \frac{(1200*10^{3} Pa)(0.5m)}{50*10^{6} MPa}[/tex]
[tex]t = 0.012 m[/tex]
[tex]t = 12 mm[/tex]
However, this is not the answer. The answer takes the longitudinal stress equation as the governing one. Therefore, the solution is half of mine, a thickness of 6 mm.
Why is this so?
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