Quick questions on Gravitation and orbital motion - TCE Physics (Tasmania)

Newton proposed that any two point masses attract each other along the line joining them with a force proportional to the product of their masses and inversely proportional to the square of their separation:

It is often more useful to describe gravity as a field. The gravitational field strength $g$ at a point is the force per unit mass placed there:

Newton's law of gravitation and Coulomb's law share the same inverse-square form, $F \propto \dfrac{1}{r^2}$, with a product of source quantities on top. The differences are instructive: gravity acts on mass, which is always positive, so it is always attractive, while the electric force acts on charge of either sign and can attract or repel. Gravity is also vastly weaker: between two protons the Coulomb force exceeds the gravitational force by about $10^{36}$ times. Recognising this shared structure lets you carry over the same ratio techniques between the two topics.