We know that momentum should be conserved
gives 0.5*2 = (1+0.5)*v
where v i the velocity of entire mass system moving after collision...
energy lost = kinetic energy of the system before collision - kinetic energy of the system aftr collision
= 1/2*0.5*22 -1/2* 1.5 *(1/1.5)2
All the best for IITJEE preparation,