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Change in GPE and Ek as object approaches a planet

  1. Jun 11, 2014 #1
    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.

    Attached Files:

  2. jcsd
  3. Jun 11, 2014 #2


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    Staff: Mentor

    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?
  4. Jun 11, 2014 #3
    Oh I see my problem. I read the graph as the magnitude increasing but realized that's wrong. Thank you.
  5. Jun 11, 2014 #4
    Only the magnitude is increasing; the negative sign before magnitude makes it decreasing.
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