im not sure if i did this problem right, something tells me i didnt do it right...could you check my work? thanks in advance.
IMG.pdf
the key here is to treat the natural length of the spring (no stretch) as
stretching the spring 5 cm beyond its natural length ...
work done to stretch the spring 10 cm beyond its natural length ...
work done to stretch the spring from 20 cm to 30 cm (from 10 cm to 20 cm beyond its natural length) ...