Chapter 10, Problem 81PQ

A Show that the total momentum of a system of particles equals the momentum of the center of mass:

${\stackrel{\to }{p}}_{\text{tot}}={\displaystyle \underset{j=1}{\overset{n}{\sum }}{\stackrel{\to }{p}}_j={\stackrel{\to }{p}}_{\text{CM}}}$    (10.8)