The length a spring stretches when subjected to the given load is required.
The spring is stretched by 18 inches.
F = Force
k = Spring constant
x = Stretched length
[tex]F=50\ \text{lbf}[/tex]
[tex]x=5\ \text{inch}[/tex]
Hooke's law is given by
[tex]F=kx\\\Rightarrow 50=k5\\\Rightarrow k=\dfrac{50}{5}\\\Rightarrow k=10\ \text{lbf/inch}[/tex]
[tex]F=180\ \text{lbf}[/tex]
For the required spring
[tex]F=kx\\\Rightarrow x=\dfrac{F}{k}\\\Rightarrow x=\dfrac{180}{10}\\\Rightarrow x=18\ \text{inches}[/tex]
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