Question

If the length of a `47` `cm` spring increases to `89` `cm` when a `2` `kg` weight is hanging from it, what is the spring's constant?

Answer 1

We should work in SI units, so the stretch is `0.89-0.47=0.42` `m`. Then we know the weight force of a `2` `kg` mass is `19.6` `N` and `F=kx`, and can rearrange to give: `k=F/x=19.6/0.42=46.7` `Nm^-1 or kgs^-2`.