Final answer:
While Yolanda is partially correct in using a sphere to model the surface area due to its minimal surface area per volume, boulders are not always spherical in nature. Real boulders may have irregular shapes influenced by numerous physical factors, including erosion and rock formation history.
Step-by-step explanation:
Yolanda is partially correct in using a sphere to model the surface area of the boulders on the beach since a sphere has the minimum surface area for a given volume. However, boulders themselves are rarely perfect spheres in nature, and the actual shape of boulders can deviate from a spherical shape depending on various factors such as erosion and the history of the rock formation.
Considering the physical principles of gravity, boulders, like any solid object, tend to have irregular shapes, especially when they are small enough that the forces holding their material together counteract the gravitational pull towards a more spherical shape. This phenomenon is more evident in celestial bodies like asteroids, where those smaller than about 400 kilometers in diameter can have almost any shape. In the case of boulders on Earth, factors such as the composition of the rocks can support non-spherical shapes. Hence, when modeling their surface area, a more complex shape that reflects the boulder's actual contours would often give a more accurate result.