Chapter 6.6, Problem 8ES

A spring whose natural length is $15\text{ cm}$ exerts a force of $45\text{ N}$ when stretched to a length of $20\text{ cm}$ .

(a) Find the spring constant (in newtons/meter).

(b) Find the work that is done in stretching the spring $3\text{ cm}$ beyond its natural length.

(c) Find the work done in stretching the spring from a length of $20\text{ cm}$ to a length of $25\text{ cm}$ .