In general sense momentum conservation is making sense to me almost everywhere but when in physics problems scenarios where all surfaces become smooth and the objects are just gliding over one another I'm not able wrap my head around the fact the one body which is moving in a way parallel to the other body (and both bodies have absolutely no friction acting between them) makes the other body move in opposite direction.
In case of explosion and sliding off a ramp the force vectors are clear and can be defined and I'm able to visualize how conservation of momentum would take place. but in scenarios like the images I've attached with this post.
like in above question(question marked as 3 and is corssed) the block of mass 2 kg does appear to move with an accelaration of 5 m/s^2 but since the pulleys and ropes are ideal and all contact surfaces are smooth how does any amount of force can make block of mass 3 kg move?
And in this one specially (question marked as 6.) motion of block B and Block A is obvious but the motion of block c seems odd. There is no force acting on block c to provide it an accelaration in any direction but yet the author put an answer to the accelaration of block c as g/7?