Ageologist is observing the side of a mountain for evidence of erosion when a large rock begins to accelerate down the mountainside. using his knowledge of the laws of physics, what change should he conclude caused the rock to accelerate? a. when stationary the force of gravity on the rock was less, and when accelerating it was greater. b. when stationary there were no forces on the rock and when accelerating there were forces on it. c. when stationary there were equal forces on the top and bottom of the rock, but not on the left and right sides. d. when stationary the rock did not have a net force on it, and when accelerating it did.