Asmall rock remains at rest in outer space while an astronaut pushes horizontally on it with a force of 20 n. which of the following must be true? a. there is another horizontal force acting on the rock. b. there are vertical forces acting on the rock. c. the rock is extremely massive. d. the rock does not feel the gravitational pull of earth.

Diego is trying to lift a piano to the second floor of his house. diego uses a pulley system and gives a big lift to the piano. the piano moves upward, then stops, and then it starts to fall to the ground. which list best describes the forces on the piano in the proper order? positive force → balanced force → negative force negative force → balanced force → positive force positive force → unbalanced force → negative force negative force → unbalanced force → positive force