# What is the work required to stretch the spring from a length of 21 inches to a length of 26 inches if a spring has a natural length of 18 inches and a force of 20 lbs is required to stretch and hold the spring to a length of 24 inches?

##### 1 Answer

This is quite a good one!

It involves the elastic force which is given by Hooke's Law as

But this is a VARIABLE force (depends on

Here

You can find

So

This is the work done by the elastic force. The work done by you to stretch the spring is the same but with opposite sign.

Please check my maths and my units as I am...metric!!!

:-)