# Universal and Gravitational Force

1. Feb 3, 2005

### Neerolyte

i have a couple questions to ask

1: When a satellite is in eclipsical orbit, the total energy should stay the same wether it is at Perigee or Apogee, neglicting friction, correct?

2: Which is larger - The total energy of the 2.00kg satellite in its 160km orbit or the total energy is its 144km orbit. Why the two answers are different?

2. Feb 4, 2005

### Mk

1: Pretty much, It depends on how eliptical the orbit is.
2: Well, of course the 160 km orbit, because earth's pull is weaker.

3. Feb 4, 2005

### Staff: Mentor

That is correct. Total energy (KE + PE) is constant.

The satellite in higher orbit has greater energy. To understand why, figure it out! Assume a circular orbit: use Newton's 2nd law for centripetal motion to find the speed and thus the KE. The PE = $-GMm/r$. Now find the total energy for both orbits and compare.