# If the length of a #21 cm# spring increases to #45 cm# when a #2 kg# weight is hanging from it, what is the spring's constant?

##### 1 Answer

Jan 8, 2017

I got

#### Explanation:

We can us Hooke's Law to relate the elastic force of a spring of elastic constant

Also, Newton's Second Law will help us to consider the forces involved through:

let us see:

So at the equilibrium the elastic force and the weight (

But the elongation is directed downwards so we write, using numbers:

So:

I changed the lengths into meters because I am used to this but if you need it in N/cm use