Two springs that are identical each have spring constant $k$. They are joined in parallel. The length of the springs when unstretched is $x$. A force $F$ is applied to the pair of springs. Their length is then $y$. Each spring is stretched only within its limit of proportionality. Which expression shows the elastic potential energy stored in one spring?
- A$\frac{1}{4}F(y-x)$
- B$\frac{1}{2}F(y-x)$
- C$\frac{1}{4}k(y-x)^2$
- D$k(y-x)^2$