What is the special k

Trail Spring strength 1 Spring strength 4 Spring strength 10 Mass Force (N) Distance(m) Mass(g) Force(N) Distance(m) Mass Force Distance 0 g O O 0 0 O 0 2 50 g 0.49 0.33 50 0.49 0.16 50 0.49 0.09 3 100 g 0.98 0.65 100 0.98 0.33 100 0.98 0.17 4 150 g 1.47 0.97 150 1.47 0.5 150 1.47 0.24 5 200 g 1.96 200 1.96 0.65 200 1.96 0.35 6 250 g 2.45 250 2.45 0.82 250 2.45 0.42 7 300 g 2.94 --- 300 2.94 300 2.94 0.5 8 green ---- 0.4 green ---- 0.2 green 0.11 9 Blue 0.77 Blue 0.4 Blue 0.21 10 Pink ---- ---- Pink ---- 0.61 Pink 0.32