Classify the waves as being mechanical

Microwave is Electromagnetic, as is radio wave, ocean is mechanical, s is seismic. A mechanical wave requires an initial energy input. Once this initial energy is added, the wave travels through the medium until all its energy is transferred. In contrast, electromagnetic waves require no medium, but can still travel through one. Electromagnetic waves or EM waves are waves that are created as a result of vibrations between an electric field and a magnetic field. In other words, EM waves are composed of oscillating magnetic and electric fields.

The mass has escaped into a gas which you can not see so the law stays true.