Asuspicious-looking man runs as fast as he can along a moving sidewalk from one end to the other, taking 2.90 s. then security agents appear and the man runs as fast as he can back along the sidewalk to his starting point, taking 10.7 s. what is the ratio of the man's running speed to the sidewalk's speed (running speed / sidewalk speed)?

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 -