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. (The direction of the force of gravity is negative.)

As the piano moves upward, Diego’s lift provides a positive force. When the piano stops, the forces are balanced, so there is no change in its motion at that moment. Once it starts falling, gravity acts downward, which the question defines as a negative force. Therefore, the correct choice is positive force → balanced force → negative force.

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