What formula should I use for this question? I'm thinking hook's law, but It doesnt seem to fit. A mass is attached to a spring that has a constant of 100 N/m. The mass vibrates with a frequency of 2 Hz. I have to find the value of the mass and how far it streaches. I know I can use hook's law for the streaching part, but I am unsure of how to carry out this problem.