Select the correct answer. what did galileo discover when he dropped two cannon balls of different weights from the leaning tower of pisa? a. the force acting on both of the balls was the same. b. the time for both of the balls to reach the ground was the same. c. a mass-dependent attractive force was exerted by earth on the two balls. d. gravity pulls everything downward. e. the balls exerted an attractive force between each other as they fell.