During a rescue mission, a plane drops a crate of emergency supplies while maintaining a constant speed and level flight. The crate makes up 10% the mass of the plane. 90% of the total mass, or the airplane,
continued on level flight, and 10% of the mass was dropped by the plane. Assume that there is no air
friction and no parachutes on the crate. Consider the system to be the plane and crate together.

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -

A) acceleration. this seems to be the one that makes sense.