Energy storage

1. superwolf

192
1. The problem statement, all variables and given/known data

2. The attempt at a solution

a) $$d = \frac{f-f_1}{k}$$

$$d = (f-f_1)d = \frac{(f-f_1)^2}{k}$$

Correct?

b) Useful work at max. when $$f_1=0$$; $$Work = \frac{f^2}{k}$$

Hm...What's wrong here?