In a one dimensional collision between two identical particles A and B, B is stationary and A has momentum p before impact. During impact, B gives an impulse J to A. Then, coefficient of restitutionbetween the two is

Let uA and uB be the velocities of A and B respectively before impact and vA and vB be the velocities of A and B after impact.Before impact, uB = 0                        p = muAAfter impact, p-J = mvA and J = mvBCoefficient of restitution, e =vB-vAuA-uB=J-(p-J)p                                            =2J-pp=2Jp-1