Answer:
The rest energy of a feather can be calculated using the equation E=mc^2, where E is the energy, m is the mass, and c is the speed of light. Since the feather is at rest, its kinetic energy is zero, so its rest energy is equal to its total energy.
The mass of the feather is 8.2x10^-6 kg. The speed of light is 299,792,458 m/s.
E = (8.2x10^-6 kg) x (299,792,458 m/s)^2
E = 7.4 x 10^-4 joules
Therefore, the magnitude of the rest energy of the feather is 7.4 x 10^-4 joules.