Applying Hooke's Law
So you have the formula F=Ks, but what are you going to do with it?
Well, let's see...
First, we've got to know how to find the K or the Elastic Constant
And we've been given the following information:
      EX1. A 5kg weight is placed on a spring and the spring is stretched     .5 meters. Then a 7kg weight is placed on the same spring and the spring is stretched 1 meter.  Finally, a 9kg weight is placed on the same spring and it is stretched 1.5 meters. Find the
Elastic Constant of the spring.
Solution:
    To find K, we will plot a graph of Force vs. Distance

Force is determined by the mass of the object times gravity (approx. 10m/s)
         ex. F= (5kg) x (10m/s)
              F= 50 kg m/s
The slope of the graph we have just created will        then be our K, the elastic constant