1. The problem statement, all variables and given/known data I am given a water tank, a small plastic cup, and some gravel. How could I use Archimede's principle to determine how much gravel to put in the plastic cup such that it sinks to a certain point (namely the rim), but then floats, so that no water is let inside the cup? 2. Relevant equations I'd imagine the most relevant equations to this problem would be those of pressure, buoyant force, mg in general, and density. I am quite unsure of where to start, let alone calculate the exact value. I have limited knowledge of buoyant mechanics, so any help would be greatly appreciated. Thank you!