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