The shape of a shockwave for a craft/object traveling through the atmosphere is a cone. Basically, the frustrum (tip) of the cone starts just at the leading edge of the object; in the case of a fighter jet, it would start at the antenna or nosecone.
This front shock is called a bow shock, and...
RTG's (like the one used on Voyager I and II, Pioneer 12, etc.) DO use a radioactive source for energy conversion. In this case, the gamma/beta/alpha kinetic energy is converted to heat (by many many collisions with a shield or the source itself), and this heat is used to run a thermionic diode...
Sound is just simply the propagation of a pressure gradient through time and space of a compressible medium. In other words, as a "sound wave" passes a region of space, the NET momentum of the collection of gas particles causes an the applied pressure gradient to exist. So, think of the...