Change in GPE and Ek as object approaches a planet

Click For Summary
The discussion centers on a misunderstanding of gravitational potential energy (GPE) in relation to distance from a mass. Initially, it was assumed that GPE increases as an object moves away from a planet, but the expected answer indicated that GPE decreases as the rocket approaches the planet. The confusion arose from interpreting the graph, which showed a negative slope, indicating a decrease in GPE. Upon clarification, it was understood that while the magnitude of GPE appears to increase, the negative sign indicates that the energy is actually decreasing. This highlights the importance of correctly interpreting the signs in physics graphs.
Saado
Messages
44
Reaction score
0
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.
 

Attachments

  • Untitled.jpg
    Untitled.jpg
    23.1 KB · Views: 499
Physics news on Phys.org
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.
 
Topic about reference frames, center of rotation, postion of origin etc Comoving ref. frame is frame that is attached to moving object, does that mean, in that frame translation and rotation of object is zero, because origin and axes(x,y,z) are fixed to object? Is it same if you place origin of frame at object center of mass or at object tail? What type of comoving frame exist? What is lab frame? If we talk about center of rotation do we always need to specified from what frame we observe?

Similar threads

  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 86 ·
3
Replies
86
Views
8K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 41 ·
2
Replies
41
Views
4K
Replies
6
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 22 ·
Replies
22
Views
771