Final answer:
The density of a rock can be directly measured by its mass and displaced volume, and the given example calculates to a density of 2.7 g/cm³, which is consistent with that of granite.
Step-by-step explanation:
The density of a rock can be determined by measuring its mass and volume. The density is then calculated using the formula: Density = Mass / Volume. Using the example given, if a rock has a mass of 240 grams and displaces 89.0 cm³ of water, the density can be calculated as follows:
Density = 240 g / 89.0 cm³ = 2.7 g/cm³
This value is consistent with the known density of granite, which generally ranges from 2.6 to 2.7 g/cm³. This suggests that the density of these rocks was indeed directly measured using this technique. Although there are more precise methods for measuring density, the mass-over-volume method is a straightforward and commonly used technique. This method of submerging the rock in a graduated cylinder is based on Archimedes' principle, which states that the volume of the displaced fluid is equal to the volume of the object.