A particle of mass m moving with horizontal speed 6 m/sec as shown in figure. If m<

v1=m1−m2m1+m2 u1+2m2u2m1+m2Substituting m1 = 0,  v1=−u1+2u2⇒v1=− 6+2(4)=2m​/​si.e. the lighter particle will move in original direction with the speed of 2 m/s.