Separation of Motion of a system of particles into motion of the centre of mass and motion about the centre of mass :
Show `p=p'_1+m_iV` where pi is the momentum of the ith particle (of mass `m_i`) and `p′_i = m_iv′_i`. Note `v′_i` is the velocity of the ith particle relative to the centre of mass. Also, prove using the definition of the centre of mass `sum p'_1=0`