When do you use G=F/m and when do you use F=(Mm)/(r^2)

case in point:

The attachment won’t load, and I think you also meant F=Gmm/r^2 as opposed to F=mg. Note the difference in capital and lower case g. Little g is the gravitational field strength, whereas big G is the gravitational constant. You use g=F/m when you want to find the field strength at a point, or find the weight a mass has. Newton’s law of gravitation is used to calculated the force of attraction between 2 objects, not the field strength (force per unit mass)

The attachment won’t load, and I think you also meant F=Gmm/r^2 as opposed to F=mg. Note the difference in capital and lower case g. Little g is the gravitational field strength, whereas big G is the gravitational constant. You use g=F/m when you want to find the field strength at a point, or find the weight a mass has. Newton’s law of gravitation is used to calculated the force of attraction between 2 objects, not the field strength (force per unit mass)

I’m referring mainly to questions 1b and 2a which equations do I use and how do I tell what to use, the answers I got don’t make sense

Gravitational attraction is always given by F=Gm1m2/r^2 so you should use that equation. The other one is to define the field strength at a given point relative to the centre of mass

For question 4a I used newtons law however for b it looks as though that was the scenario I was meant to use it. Notice how it the masses are quoted under it?

I’m a little confused, I don’t think I’m doing this correctly. Here’s what I wrote anyways.