The correct options are
A Velocity of centre of mass will be m2v0m1+m2
D Maximum elongation that the spring will suffer xmax=√m1m2k(m1+m2).v0
Given, Initial velocity of m2=v0
Initial velocity of m1=0
As we know, Vcom=m1v1+m2v2m1+m2
Vcom=m1(0)+m2(v0)m1+m2=m2v0m1+m2
The spring will have maximum elongation when velocities of both blocks will attain the velocity of COM of the two blocks.
As we know,
Change in KE = Potential energy stored in the spring.
Assume xmax= maximum elongation in the spring
Hence, KEi−KEf = Potential energy stored
12m2v20−[12(m1+m2)v2com]=12kx2max
⇒12m2v20−[12(m1+m2)(m2v0m1+m2)2]=12kx2max
⇒m2v20[1−m2m1+m2]=kx2max
⇒xmax=√m1m2k(m1+m2)v0