A 50,000 kg plane is flying at a constant velocity of 130 m/s. Is the plane in a state of equilibrium

yes

Explanation:

Equilibrium means that all the forces acting upon the object are balanced. A cruising airplane has all four forces balanced, with no external forces acting on it. As a result it will remain in its motion at a constant velocity until an external force acts upon it

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.