If a spring has a constant of #8 (kg)/s^2#, how much work will it take to extend the spring by #40cm #?
Consider your system,
Recall Hooke's Law,
Moreover, recall that work is represented by,
(the reason this is halved is because we're averaging the force)
To be sure, the elastic potential energy is equal to the work done to stretch it that far (which shares the same equation as that derived).