"3 PHYSICAL SCIENCE: In order to figure out what is in a sealed box, you perform some tests. The box seems heavy for its size and is harder to remove from a steel table than when placed on a concrete floor. What kind of object could be inside the box?"
A large magnet. A magnet, regardless of type, is quite heavy. Especially if it's a rather dense one because it'll weight more because of more mass occupying a small space. It's a magnet because of the box's attraction to the steel table rather than concrete. Magnets attract metals instead of concrete.