The spring constant is:
[tex]\Large\displaystyle\text{$\begin{aligned}k &= 612.5\ \dfrac{\text{N}}{\text{m}}\end{aligned}$}[/tex]
To calculate the spring constant we must remember the law for it, the Hooke's Law:
[tex]\Large\displaystyle\text{$\begin{aligned}\vec{F} = -k\Delta \vec{x} \end{aligned}$}[/tex]
Where k is the spring constant [N/m].
So if the mass is suspended it means that its weight is equal to the elastic force (values), then we can write:
[tex]\Large\displaystyle\text{$\begin{aligned}\vec{W} = k\Delta \vec{x} \end{aligned}$}[/tex]
Therefore:
[tex]\Large\displaystyle\text{$\begin{aligned}mg &= k\Delta x \\ \\k &= \dfrac{mg}{\Delta x} \\ \\\end{aligned}$}[/tex]
Now we just have to put the values and calculate:
[tex]\Large\displaystyle\text{$\begin{aligned}k &= \dfrac{mg}{\Delta x} \\ \\k &= \dfrac{5\cdot 9.8}{0.08} \\ \\k &= 612.5\ \dfrac{\text{N}}{\text{m}}\end{aligned}$}[/tex]
I hope you liked it
Any doubt? write in the comments and I'll help you
