A plutonium-242 atom has a nucleus of 94 protons and 148 neutrons and has 94 electrons. The diameter of its nucleus is approximately 15 × 10 − 15 m . (a) Make a reasonable physical argument as to why we can treat the nucleus as a point charge for points outside of it. (b) Plutonium decays radioactively by emitting an alpha particle from its nucleus. The mass of the alpha particle is 6.6 × 10 − 27 kg , and the particle has two protons and two neutrons. If the alpha particle comes from the surface of the 242Pu nucleus, what is its greatest acceleration?