how do i work these forces calculations out, i don't understand how to work it out it's very confusing!

Question

The table shoes the total length of a spring when different loads are applied


Load in N Total length in cm
2 12
3 15


a. what extension is produced in the spring by a load of 1N?
b. calculate the origional length of the spring.

Answer 1

It looks from the data that when the load on the spring gets 50% more (from 2 to 3), the spring gets longer by 25% (from 12 to 15)
Assuming the spring acts this way in a linear manner, a load of 1 will produce a spring length that fits this formula
L + (L * .25) = 12
1.25 L = 12
L = 12 / 1.25 = 9.6

for part b, draw a graph of length on the x axis and force on the y axis with the values you now have.
The point where the line crosses the y axis is the original length.

Answer 2

F=kx
Since the difference between 3 N and 2 N is One Newton and the displacement is 3cm the extention for a 1 N load would be 9 cm and the original length 6 cm