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**1. The problem statement, all variables and given/known data**

A series of masses are hung from a vertical spring and the length is measured in each case to the nearest milimeter. Data below:

__Mass : Spring Length__

050g : 40.2cm

100g : 45.8cm

150g : 50.9cm

200g : 56.4cm

250g : 61.4cm

300g : 66.9cm

350g : 73.7cm

400g : 81.2cm

I need to find the spring constant.

**2. Relevant equations**

F

_{s}= k | l - l

_{0}| ,

where

F

_{s}= Spring Force

k = spring constant

l = length of spring

l

_{0}= initial length of spring

**3. The attempt at a solution**

I know that F

_{s}= F

_{g}= mass / 100 (using g = 10 N/kg).

I just don't know how to get the constant because I don't know what the initial spring length is (it's not 0).