A block of mass 0.5 kg  is moving with speed of 2 m/s on a smooth surface.  It strikes another mass of 1 kg and then they move together as a single body.   The Energy loss during the Collision is,

apply law of conservation of linear momentum pbefore=pafter mu = (m+M)V m=0.5kg;M=1kg;u=2m/s 0.5(2)=(0.5+1)V V=11.5m/s KEinitial=12mv2=12x0.5x22=1 joule KEfinal=12mv2=12(1.5)(11.5)2=0.33 joule loss of KE=KEinitial-KEfinal=1-0.33=0.67 joule