These is my problem Assuming the surface on which A rests is frictionless and there is no drag on either of the bodies as they move at common acceleration. Correct me if I’m wrong, I think the bodies should have a common acceleration since they’re connected Why does F? exist??, I know that F? is exerted on the body B such that the net force on B downwards is less than mg but what is causing this force?, Looks to me like this force is a pull on the string by A but I don’t think there is any force acting to the left of body A besides friction and drag which I have assumed to be non-existent. I would be grateful on getting well explained answer...Help me guys.