  At time zero, there are $N$ identical point particles in the line (1D) which
are characterized by their positions and velocities. Both values are given
randomly and independently from each other, with arbitrary probability
densities. Each particle evolves at constant velocity until eventually they
meet. When this happens, a perfectly-plastic collision is produced, resulting
in a new particle composed by the sum of their masses and the weighted average
velocity.
  The merged particles evolve indistinguishably from the non-merged ones, i.e.
they move at constant velocity until a new plastic collision eventually
happens.
  As in any open system, the particles are not confined to any region or
reservoir, so as time progresses, they go on to infinity.
  From this non-equilibrium process, the number of (now, non-identical) final
particles, $\tilde{X}_N$, the distribution of masses of these final particles
and the kinetic energy loss from all plastic collisions, is studied. The
principal findings shown in this paper are outlined as follows: (1) A method
has been developed to determine the number and mass of the final particles
based solely on the initial conditions, eliminating the need to evolve the
particle system. (2) A similar model of merging particles, with a universal
number of final particles, $\tilde{Z}_N$, is introduced. (3) Strong evidence
that $\tilde{X}_N$ is also universal and has the same law of probability as
$\tilde{Z}_N$ is presented. (4) An accurate approximation of the energy loss is
presented. (5) Results for $\tilde{X}_N$ for an explosive-like initial
condition are analyzed.
