Asolid ball with mass m and radius r is rolling (without slipping) on a flat surface at 6 m/s. it then gets to a small smooth hill and rolls up 80 cm to the top and continues rolling on a flat surface. (a) explain why we are allowed to apply the conservation of energy to the ball although rolling requires friction. (b) use conservation of energy to find the velocity of the ball after it has passed the hill. (moment of inertia of a solid ball around its center of mass is 2 5 mr 2

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 -