A) The mass of the rock B) The weight of the rock C) Both the mass and the weight are important. D) Either the mass or the weight, as they are related by a single multiplicative constant, g.
Similarly, if the large rock merely sits on your toe, which concept is most important in determining how much it hurts?
For a falling rock, to me it seems that mass would be most important as the pain level would be proportional to the change in momentum, or the impulse, on your foot.
For a stagnant rock, it seems either weight or mass would be the same.
Am I correct?