In this paper linear time-invariant dynamical systems described by a combination of differential equalities and static inequalities in state-space formulation are investigated, Of special interest is the contact problem : the effect of the boundary of the constraint set on the behavior of the system, This effect is studied by dividing the state-space in a number of disjunct subsets, It is shown that these subsets are invariant under linear state feedback, In our framework, a specific place is reserved for modeling the laws of collision, i.e., physical modeling, which are regarded as external factors, Our main results are a system theoretical framework in which we describe what happens upon contact and a definition of the constrained state-space system in terms of its restricted behavior, The results presented here can be considered as an extension for restricted linear systems of the classic positive invariance theory for linear systems.