What weighs 100 tons?

A ton is a measure of mass, not of weight. A truck may have a mass of 5-10 tonnes (or more, if it is a very large truck), so gather a few of those, and you have 100 tonnes. Another example would be 100 cubic meters of water (for example, the contents of a rectangular 5x10 swimming-pool, with a depth of 2 meters).