phy53 dr. brown 30 sep 2010 collisions in 2, 3 - D often leads to more unknowns than equations -- Elastic collisions momentum AND K conserved -- totally Inellastic momentum conserved -- but NOT K same for partially inellastic example ellastic collision solve in center of mass frame -- "easiest" way v_lab = v_cm + u review inellastic collision K in and out of the CoM frame K-lab = K of cm + K in cm Rigid objects disk translation and rotation