current or voltage we measure for AC are alaways rms(root mean square) value not the actual magnitude so 220 volt ac(rms)= 220*sqrt(2)=311 volt but 220 volt DC alaways gives the magnitude...
There are 3 Types of Collisions Elastic, Inelastic and Totally Inelastic collision. Momentum is conserved in all these three types ( No external force is involved, so the system is called a Closed System....