AL Physics 2008 MCQ6

By conservation of momentum,
2(0.5)+3(0)=(2+3)v
so, v=0.2ms^-1
since maximum EPE occurs when two blocks moves with same speed together,that is no more compression on the spring.so maximum EPE occurs when v=0.2ms-1
Since collision is elastic,no energy is lost
By conservation of mechanical energy,
1/2(2)(0.5)^2=1/2(2+3)(0.2)^2+EPE
so max EPE=0.15J

the anser is B