Physics: Work 2?

Question

A certain spring is extended from x=0 to x=4 cm. It was previously found that a force of 70 Nt was required to extend the spring from x=0 to x=2 cm. How much work is done?

Answer 1

The spring equations are:

F = -kX
E = (1/2) k X^2

The first says that the force is proportional to the displacement (change in length for a linear spring)

The second says that the energy in a spring is proportional to the square of the displacement.

The "k" in the two equations is a the "spring constant" of the spring.

http://en.wikipedia.org/wiki/Hooke%27s_law

Using the first equation, and the data from the 2 cm extension, you can compute the spring constant.

Using the spring constant and the energy equation, you can compute how much work was done extending the spring 4 cm.