In a vacuum, where there is no air resistance, both the large heavy rock and the small pebble would fall at the same rate and hit the ground at the same time. This is due to the principle of gravity, which pulls all objects toward the Earth with the same acceleration (approximately 9.81 m/s²) regardless of their mass.
However, if the experiment is conducted in the presence of air, the outcomes would be different. The heavy rock, being larger and denser, would experience less relative air resistance compared to the small pebble, allowing it to fall faster. The pebble, being lighter and having a larger surface area relative to its mass, would be more affected by air resistance and might float or drift down slowly.
In summary, in a vacuum, both would fall and land simultaneously; in air, the heavy rock would likely reach the ground first.