# Gravitation energy 4

1. Jun 23, 2014

### Karol

1. The problem statement, all variables and given/known data
A satellite orbits at radius r1. What is the energy required to pass it to a greater radius r2. express in terms of m and g

2. Relevant equations
The total energy of a satellite: $E=-\frac{GMm}{2r}$

3. The attempt at a solution
$$E=-\frac{GMm}{2r_2}+\frac{GMm}{2r_1}=-\frac{RGMm}{R2r_2}+\frac{RGMm}{R2r_1}=\frac{Rgm}{2}\left( \frac{1}{r_1}-\frac{1}{r_2}\right )$$
$$\frac{R^2gm}{2}\left( \frac{1}{r_1}-\frac{1}{r_2} \right)$$

2. Jun 23, 2014

### Orodruin

Staff Emeritus
A good first check is to make sure that the physical dimensions are consistent in every step. Your answer has dimensions energy/length and is therefore wrong. I suggest controlling the intermediate steps.

3. Jun 23, 2014

### Karol

I found the mistake, Thanks, it helped