A particle of mass m collides with another stationary particle of mass M. If the particle m stops just after collision, then the coefficient of restitution for collision is equal to

As, net horizontal force acting on the system is zero, hence momentum must remain conserved.Hence,                     mu + 0 = 0 + Mv2⇒                                       v2=muMCoefficient of restitution, e=v2-v1u2-u1=v2-0|0-u|                                          =v2u=muMu=mM