  In this paper, we study the Riemann solutions for two systems: the
nonsymmetric Keyfitz-Kranzer system and the pressureless system, both of which
have a time-dependent Coulomb-like friction term. Our analysis identified two
types of Riemann solutions: contact discontinuities and delta-shock solutions.
We obtain generalized Rankine-Hugoniot conditions, which is the support for
constructing the delta-shock solution for the nonsymmetric Keyfitz-Kranzer
system with a time-dependent Coulomb-like friction term. Furthermore, we
demonstrate that as the pressure tends to zero, the Riemann solutions of the
nonsymmetric Keyfitz-Kranzer system converge to those of the pressureless
system, with both systems incorporating a time-dependent Coulomb-like friction
term.
