# Homework Help: Help with problems!

1. Jul 23, 2006

### Mateja

Can you help me with solving this few problems>

1. Satellite is orbiting above the Mars at 6 600 km above the surface. On the satellite are solar discs who are gathering energy from Sun. If the surface of all discs is 50 m^2, estiamte how much time is enough to satellite gath enough energy to live gravitational field of Mars. How much time (n) satellit orbits the planet for this time? Part of energy that accumulate is 80% of energy of Sun radiation that falles on the discs. Level of orbite, and solar discs of satellite are always normal on direction Mars-Sun. Mmars = 0,64 x 10^24 kg, Rmars = 3 395 km, Msatellite = 3 000 kg, G = 6,67 x 10^-11 Nm^2\kg^2

the rest problems I will post later...

Last edited: Jul 23, 2006
2. Jul 23, 2006

### HallsofIvy

This looks like homework so I am moving it. Also, Mateja, you must post what you have done on this so we will know what kind of help you need.

3. Jul 23, 2006

### HallsofIvy

Enough energy for what? I don't see what the gravitational field has to do with "enough energy" for anything.

4. Jul 23, 2006

### Mateja

Energy that satellit accumulate must be bigger or equal with gravitational potential energy of Mars, so satellit can leave gravitational field of Mars.

Satellit on circuling around the Mars have energy -G*M*m/(2*a) where a is the semimajor axis of orbit = Rmars + h. Than i dont know hot to get energu from sun radiation, but then i probably must multiplie that energy with 0,8 (80%) and equal it with energy -G*M*m/(2*a). From T=2*pi*a/v, v=sqrt G*M/a and n=t/T i get n. i have two problems

1. how to get energy of sun radiation
2. wath will hapen when satellite is in mars shadow