# If the length of a 38 cm spring increases to 64 cm when a 4 kg weight is hanging from it, what is the spring's constant?

We know.if by applying force $F$ we can cause $\partial x$ amount of increase in the length of a spring,then they are related as $F = K \partial x$ (where, $K$ is the spring constant)
Given, $F = 4 \cdot 9.8 = 39.2 N$ (as,here the weight of the object is the force which causes this extension)
and , $\partial x = \frac{64 - 38}{100} = 0.26 m$
so, $K = \frac{F}{\partial x} = \frac{39.2}{0.26} = 150.77 N {m}^{-} 1$