Elastic collisions are collisions in which both momentum and kinetic energy are conserved. The total system kinetic energy before the collision equals the total system kinetic energy after the collision. We calculate as follows:
m1v1 = m1v1' + m2v2'
0.80(0.50) = (0.80)(0.80-1)/(0.80+1)(0.50) + 1v2'
v2' = 0.11
Hope this helps. Have a nice day.