Energy loss of fast N(S-4) atoms in a bath gas of N-2 molecules is investigated taking into account elastic and inelastic collisions. Quantum mechanical calculations using a vibrationally close-coupled rotationally sudden approach are performed to obtain the elastic scattering cross sections. Inelastic cross sections involving re-vibrational transitions of the molecules are determined from a quantum-classical approach in which the vibrational motion of the molecule is treated by the time-dependent quantum mechanical method and the remaining degrees of freedom described by classical mechanics. The computed angular and energy resolved cross sections are used to construct the Boltzmann kernel for energy relaxation of fast N(4S) atoms from which the parameters governing the thermalization are readily extracted.