[quote=@SirBeowulf]
The chain probably can't withstand the full force of a box colliding with it, is what I was going for. If he was lucky, and the box went in straight collided straight with the loop, it would be likely that the small chains couldn't fully handle the impact and just tore apart. That is, unless the teacher actually went and used a large size chain to hold it up there, which I wouldn't really imagine. 
[/quote]

I don't know what kind of chain you've been exposed to but most of the ones I've seen wouldn't break if someone hit them straight on with a single well aimed shot put ball (which would be about equal in weight to that of the cube). Ignoring that point for one moment if I was the teacher and in position of chain that could be broken by someone hitting it with a thrown cube that I was providing I would expected some dumbass to try so I would then go down to the Remnant hardware store and buy chain that doesn't shatter like glass.