An inventive child named nick wants to reach an apple in a tree without climbing the tree. sitting in a chair connected to a rope that passes over a frictionless pulley (fig. p4.45), nick pulls on the loose end of the rope with such a force that the spring scale reads 250 n. nick's true weight is 320 n, and the chair weighs 160 n. nick’s feet are not touching the ground. (a) draw a pair of diagrams showing the forces for nick and the chair considered as separate systems and another diagram for nick and the chair considered as one system. (b) show that the acceleration of the system is upward and find its magnitude. (c) find the force nick exerts on the chair.

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 -

Clike bone scan for find heart