Why is acceleration measured in meters / seconds squared?

This is because to find acceleration, you must divide velocity by time. Velocity is measured in meters / second, and time is measured in seconds. So, when meters / second is divided by seconds, the units become meters / second squared.

Hope this helps

Tobey

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.