Question

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.) 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

Explanation:

1. When Diego lifts the piano (positive force, opposite to gravity's negative), the piano moves up (unbalanced force as net force isn't zero).
2. When it stops, forces are balanced? No, wait—first, lift (positive force, unbalanced as piano moves up). Then stops (momentarily balanced? No, actually, when moving up, positive force > gravity (negative). Then stops (maybe force becomes balanced? No, the options have positive → unbalanced → negative? Wait, no—wait, initial lift: positive force (Diego's) is greater than gravity (negative), so unbalanced (piano moves up). Then when it stops, maybe force becomes balanced? No, the options: let's re-examine. Wait, the first action: Diego's lift is positive (opposite to gravity's negative). The piano moves up: unbalanced force (since it accelerates up). Then it stops (momentarily), then falls: gravity (negative) becomes greater, so negative force. Wait, the correct option: positive force (Diego's lift) → unbalanced force (piano moves, so net force non - zero) → negative force (gravity takes over, piano falls). So the option "positive force → unbalanced force → negative force" is correct.

Answer:

positive force → unbalanced force → negative force