F=kx----> K=F/x
K=0.1/0.002 = 50 N/m
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Compressione $\delta= 0,20\,cm = 0,002\,m;$
forza $F= 0,10\,N;$
costante elastica della molla $k= \dfrac{F\,(N)}{\delta\,(m)} = \dfrac{0,10}{0,002} = 50\,N/m.$
costante elastica k = F/x = 0,1 N/0,002 m = 100/2 = 50 N/m