Change in GPE and Ek as object approaches a planet

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Discussion Overview

The discussion revolves around the concepts of gravitational potential energy (GPE) and kinetic energy (Ek) as an object approaches a planet. Participants explore the relationship between these energies in the context of classical physics, particularly focusing on the interpretation of a graph related to GPE and its behavior as the object moves closer to the planet.

Discussion Character

  • Conceptual clarification, Technical explanation

Main Points Raised

  • One participant initially assumed that gravitational potential energy increases as an object moves further away from a mass, but encountered a question suggesting otherwise.
  • Another participant pointed out that the expected answer indicated GPE decreasing as the object moves closer to the planet, noting the negative slope of the curve in the graph.
  • A later reply acknowledged a misunderstanding regarding the interpretation of the graph, clarifying that the magnitude of GPE is increasing while the actual value is decreasing due to the negative sign.
  • It was noted that only the magnitude of GPE is increasing, while the value itself is decreasing as the object approaches the planet.

Areas of Agreement / Disagreement

Participants initially had differing interpretations of the graph, but there was a subsequent clarification regarding the nature of the GPE and its magnitude. The discussion reflects a resolution of misunderstanding rather than a consensus on the underlying concepts.

Contextual Notes

The discussion highlights potential confusion regarding the interpretation of graphs in physics, particularly in relation to the signs of energy values and their magnitudes. There may be assumptions about the definitions of gravitational potential energy that are not explicitly stated.

Saado
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This is not a homework question.

Whilst looking over at previous exam papers on classical physics, I came across this question in the attachment. I always assumed gravitational potential energy increased as you moved further away from a mass. But the expected answer to this question shows the GPE increasing as the rocket gets closer to the planet. I'm assuming the increase in kinetic energy is due to the field strength of the planet but I can't get my head around why the magnitude of the potential energy is increasing instead of decreasing as the object moves closer to the planet.
 

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The expected answer in the attached thumbnail shows the gravitational potential energy decreasing (slope of curve is negative) as the ship moves from A to D and then remaining constant. Where do you see anything increasing in that curve?
 
Oh I see my problem. I read the graph as the magnitude increasing but realized that's wrong. Thank you.
 
Only the magnitude is increasing; the negative sign before magnitude makes it decreasing.
 

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