Using the law of conservation of momentum m1u1+m2u2=m1v1+m2v2 Where m1 is mass of first object m2 is mass of second object u1 and u2 are initial velocities of object 1 and 2 respectively v1 and v2 are final velocities of object 1 and 2 respectively Here, they are moving as a system after collision. Thus they will posses same final velocity m1u1 +m2u2=v(m1+m2) Substituting values 600*4+0=v(600+400) 2400=v*1000 v=2.4 m/s
Now momentum of system p=Mv p=(600+400)*2.4 p=1000*2.4 Therefore p=2400 kg m/s Hope this helps :)
