Potential Energy Clarification

AI Thread Summary
When lifting a ball from a lower height to a higher one at constant velocity, the potential energy of the system, which includes both the ball and the Earth, increases. The kinetic energy remains constant since the velocity is constant, making statement 2 incorrect. The work done by the Earth is not negative, as it acts in the direction of the ball's movement, contradicting statement 3. The concept of gravitational potential energy applies to the interaction between the Earth and the ball, confirming that statement 1 is indeed correct. Therefore, the discussion concludes that the potential energy of the system increases when considering both the Earth and the ball.
MyNewPony
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You lift a ball at constant velocity from a height hi to a greater height hf . Considering the ball and the Earth together as the system, which of the following statements is true?

1. The potential energy of the system increases.
2. The kinetic energy of the system decreases.
3. The Earth does negative work on the system.
4. You do negative work on the system.
5. The source energy of the ball increases.
6. Two of the above.
7. None of the above.

Am I right in thinking that neither 1 nor 2 are correct because the question takes into account BOTH the Earth and the ball? They would only be correct if the system was merely the ball, right?
 
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I believe you are right there.
 
MyNewPony said:
Am I right in thinking that neither 1 nor 2 are correct because the question takes into account BOTH the Earth and the ball? They would only be correct if the system was merely the ball, right?
No, gravitational potential energy is a joint property of Earth and ball (since gravity is an interaction between them). So #1 is correct.
 

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