Answer:
720 pounds per square inch
Explanation:
If the stress in the material varies jointly with the internal pressure and the internal diameter and inversely with the thickness of the pipe, we can write the following equation
[tex]S=k\frac{PD}{T}[/tex]Where S is the stress, P is the internal pressure, D is the diameter, T is thickness, and k is the constant of proportionality.
Then, we know that S = 100 when D = 5, T = 0.75 and P = 25. Replacing the values and solving for k, we get:
[tex]\begin{gathered} 100=k\frac{25(5)}{0.75} \\ \\ 100=k(166.667) \\ \\ \frac{100}{166.667}=k \\ \\ 0.6=k \end{gathered}[/tex]Now, the equation for the stress is
[tex]S=0.6\frac{PD}{T}[/tex]So, we can calculate the strees when P = 80, D = 3 and T = 0.2 as follows
[tex]\begin{gathered} S=0.6\cdot\frac{80(3)}{0.2} \\ \\ S=720 \end{gathered}[/tex]Therefore, the answer is 720 pounds per square inch