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 $72 \mathrm {~km} \mathrm {~h} ^ { - 1 }$ 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 $\_\_\_\_$ $\times 10 ^ { 5 } \mathrm {~N} \mathrm {~m} ^ { - 1 }$.
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 $72 \mathrm {~km} \mathrm {~h} ^ { - 1 }$ 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 $\_\_\_\_$ $\times 10 ^ { 5 } \mathrm {~N} \mathrm {~m} ^ { - 1 }$.