An engineer is investigating the properties of a "2 mi/h (3 km/h) spring". He finds that it can compress elastically without permanent deformation if a heavy object of mass 1500 kg hits it with speeds below 3 km/h. In that case, the maximum compression before the spring begins to permanently deform (up to which point the behavior of the spring is elastic) is 2.3 cm. Calculate the effective spring constant of the spring.