1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Ratio between change in Energy(Gravitational Potential)

  1. Oct 4, 2008 #1
    Ratio between change of Energy(Gravitational Potential)

    I would like some assistance in understanding the ratio of change in energy between two objects.

    In this case, if object A goes from rest to an altitude (h) above earth but does not begin an orbit versus object B goes from rest to the same altitude and then proceeds to orbit the earth.

    The variables are as follows:
    Re=radius of earth
    G=universal gravitational constant
    M=mass of earth
    m=mass of object(A=B, also known as A and B are the same)

    I'll need to transcribe my findings, which until now when comparing to my professors simplication are slightly off, a little later.

    I was told my error might occur in the initial change of energies for the respective objects, and this may very well be true. However, I did come across great challenges at first when trying to find a GCF for the variable laden energies.

    What I've been using prior to simplication:
    Object A = change in Eg = Eg2 - Eg1
    Object B = change in total energy = Ek - Eg1

    Eg as known is a negative value while Ek is positive.

    Any help is appreciated and I understand little help may be offered since I've yet to put up the actual attempts, but when I have more time I'll transcribe my most recent effort into mspaint.
    Last edited: Oct 5, 2008
  2. jcsd
  3. Oct 5, 2008 #2
    A good turnout.
    Ok, here's my most recent work.

    http://img410.imageshack.us/img410/3044/ratioworkingqk8.png [Broken]

    Am I not correct in choosing the E2 and E1 for the object heading into orbit?
    I choose Total Orbital Energy (-Ek) since that is energy required to orbit for object B. Although, wouldn't it be possible to put change of energy for the object heading to altitude h as simply Ek instead of -Ek-(Eg)? I would really like some input on this.

    Also, it's been a long time since I did any Calculus and or math in general, which may explain why I have trouble with simplification.

    Some ratios, albeit told as wrong by my professor include:

    http://img296.imageshack.us/img296/3913/resultseh6.png [Broken]

    With the last in the line being the earliest example and least correct.

    As mentioned, the first two were said to be nearly correct, although it's been a few days since I spoke to her so I cannot say which is more correct.

    Again, help is appreciated. Thank you.
    Last edited by a moderator: May 3, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook