An engine is attached to a wagon through a shock absorber of length 1.5 m . The system with a total mass of $40,000 \mathrm{~kg}$ is moving with a speed of $72 \mathrm{kmh}^{-1}$ when the brakes are applied to bring it to rest. In the process of the system being brought to rest, the spring of the shock absorber gets compressed by 1.0 m . If $90 \%$ of energy of the wagon is lost due to friction, the spring constant is $\_\_\_\_$ $\times 10^5 \mathrm{~N} / \mathrm{m}$.