If the length of a #42 cm# spring increases to #87 cm# when a #1 kg# weight is hanging from it, what is the spring's constant?
Hooke's Law states that the elongation or compression of an elastic spring is directly proportional to the resultant force acting on it and in the direction of the resultant force.
So in this case, the resultant force is the weight force
The elongation in this case is
Therefore by Hooke's Law, the spring stiffness constant may be given by
(This is quite a small value, indicating a very elastic spring, easy to stretch and compress. Not very stiff).