When we say that the weight of an object is Mg, and that g = 9.8 N/kg, what assumptions are we making?

Which of the below?

-The distribution of mass in the earth is spherically symmetric.
-The density of the earth is the same everywhere.
-The earth's interior is solid everywhere.
-The orbit of the earth is circular and not elliptical.
-We neglect the effect of astronomical bodies other than the earth.
-The object is at the earth's surface.
-Two significant figures are sufficient.
Newton's law of gravitation holds.

The object is at the earth's surface.

When we say that the weight of an object is Mg, where g is the acceleration due to gravity equal to 9.8 N/kg, the assumptions we are making are as follows:

1. The distribution of mass in the Earth is spherically symmetric: This assumption implies that the Earth's mass is evenly distributed around its center, allowing us to treat the gravitational force as if it is acting from a single point at the center of the Earth.

2. The density of the Earth is the same everywhere: Although the Earth's density may vary slightly from one location to another, this assumption implies that any variation in density is negligible and does not significantly affect the calculation of weight.

3. The Earth's interior is solid everywhere: This assumption implies that the mass that contributes to the gravitational force is uniformly distributed throughout the Earth, without any significant voids or variations in density.

4. We neglect the effect of astronomical bodies other than the Earth: This assumption means that we are considering the gravitational force exerted by the Earth alone and ignoring the gravitational influence of other celestial bodies such as the Moon, Sun, or nearby planets. This simplification is often valid for most everyday calculations as the gravitational force due to other bodies is typically much smaller.

5. The object is at the Earth's surface: This assumption implies that the object is near the surface of the Earth, where the gravitational acceleration remains relatively constant and can be approximated as g = 9.8 N/kg.

6. Two significant figures are sufficient: This assumption suggests that the level of precision required in the calculation does not necessitate using more than two significant figures. This is often the case in everyday scenarios, but it may vary depending on the specific context or application.

7. Newton's law of gravitation holds: This assumption asserts that the fundamental principles of the gravitational force, as described by Newton's law of gravitation, are applicable. This law states that the force between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

It's important to note that these assumptions are necessary simplifications to make calculations easier and more practical in most situations.