Orbital speed is the speed with which a planet moves around the sun. The speed is determined by:

a)the mass of the planet only
b) the mass of the sun only
c)both the mass of the planet and the mass of the sun
d)the mass of the planet and it's distance from the sun
e) the mass of both the planet and the sun and the distance between the two

I'd guess E, but I honestly don't know.

Your intuition is correct. The correct answer is E.

The orbital motion depends upon the SUM of the planet and sun's masses. The planet's mass is usually negligible compared to its sun.

The correct answer is d) the mass of the planet and its distance from the sun.

The orbital speed of a planet is determined by both the mass of the planet and its distance from the sun. The mass of the planet affects the gravitational force between the planet and the sun. The greater the mass of the planet, the stronger the gravitational force, which results in a greater orbital speed.

On the other hand, the distance from the sun also plays a crucial role. If the planet is closer to the sun, the gravitational force experienced by the planet is stronger, leading to a higher orbital speed. Conversely, if the planet is farther from the sun, the gravitational force is weaker, resulting in a lower orbital speed.

To determine the orbital speed of a planet, you can use Kepler's third law of planetary motion, which states that the square of the orbital period of a planet is proportional to the cube of its average distance from the sun.

The formula to calculate the orbital speed of a planet is:

v = 2πr / T

Where:
- v is the orbital speed of the planet
- r is the average distance between the planet and the sun
- T is the orbital period of the planet

From the available options, the correct answer is option d) the mass of the planet and its distance from the sun. This is because the orbital speed depends on the distance between the planet and the sun, which is represented by the average distance 'r' in the formula. The mass of the planet does not directly influence the orbital speed, but it does affect the gravitational force between the planet and the sun, which in turn affects the shape and size of the orbit.

Therefore, while the mass of both the planet and the sun, as well as the distance between the two, do have an influence on the orbital dynamics, the direct factor that determines the orbital speed is the mass of the planet and its distance from the sun.