From my point of view, it seems that a soldier armed with a full metal plate armor was almost invulnerable at the time their opponents yielded swords, spears or bows. I understand that it couldn't be the case, but I'm not sure about the physics behind it.
How could an archer beat this soldier? Would it matter whether the archer aimed at more vulnerable spots at the soldier, or any arrow shooted with full power would do?
How could a swordsman or a spearman beat this soldier? Would the impact of these weapons suffice?
Just out of curiosity, a modern gun would penetrate into the plates that easily? One headshot would do?
I'm thinking on a soldier wearing an armor like this one below, or even more bulkier.
 Courtesy of Wikipedia