No oddly enough hair cannot be dissolved in stomach acid because of the way hair is made.
Stomach acid can dissolve metal but any plastic or hair will just come out in your poop if you eat the hair.
Stomach acid only has a PH of about 2, which means that it is roughly as acidic as lemon juice.
Most of the stomach's digestive ability comes from the physical process of churning up the food and breaking it apart.
Hair is flexible and strong enough that the acid and the churning have little to no effect on it.
So the end result is that if you eat hair the hair eventually goes through your stomach and into your intestines and then mixes with your poop.
Then whether you notice it or not the hair comes out in your poop.