A ball of mass 100 g is dropped from a height h = 10 cm on a platform fixed at the top of vertical spring (as shown in figure). The ball stays on the platform and the platform is depressed by a distance $\frac{\mathrm{h}}{2}$.The spring constant is ________ $\mathrm{Nm}^{-1} \cdot\left(\right.$ Use $\left.\mathrm{g}=10 \mathrm{~ms}^{-2}\right)$