approach to d prob:

see if d velocity is too high ..

they will never meet.

hence we have to find d minimum vel that must be given so that they touch each other and satisfy one more condition >>>> key word is "just able to "

so when the first block starts moving ...the other one attracts it ...which causes decrease in velocity ..

so ultimately ..we have to find that vel ..which makes d system at rest in d end...

i leave remaining for u ..u can do it from here

kehna padega ...nice question dude...