If a permanent magnet is dropped or struck by a hammer, it may loose it's magnetism. explain why.

This is because strong vibrations will affect the alignment of the magnetic domains within the magnetic material. The domains would change the alignment thus affecting the strength of the magnets which solely depends on the alignment of the domains. The strength of a magnet is the sum of the magnetic fields of all the domains in the magnet. Therefore, the net result will be a weaker magnet or the magnet loosing its magnetism.