The momentum of a system of particles is the sum of all their individual momentum (vectors): one for each particle in the system. Suppose you have a system of total mass 7.0kg, initially at rest, which "explodes" into two pieces. If one piece has mass 5.0kg and moves off with speed 4.0 m/s after the explosion, what is the speed of the other piece in SI units? Answer in m/s (without writing the unit). Hint: the initial momentum was zero, and momentum is conserved!
