I fail to understand how compartmentalization explains this. I got the answer right the first time. And I suspect most people who go it wrong did so because of the assumptions (unwarranted) they were making - meaning if they had just looked at the question and nothing else, and if they understood basic gravity, they would've got it right. But when you also try to imagine some hypothetical forces on the surface of the moon or relate to zero gravity images seen on tv etc, and if you visualize all these before you visualize the question, you'd probably get it wrong.