# In a perfectly elastic relativistic collision, which one of the following quantities is not conserved: a)Momentum b)Energy c)Rest mass d)Angular momentum In non relativistic elastic collisions, energy and momentum will be conserved. But I don’t know about relativistic elastic collisions. Could anyone please clear my doubt? Can we apply the Newtonian concepts in these cases? Suppose the collision is inelastic (relativistic), then which quantity will be conserved?