Answer 1

when you want to use same methods on many different objects. example : you have many tipes of tv, but every one of them can volume up or dawn. immagine that you have for every class of tv - sony, samsung, bosch... to write out same command to volume up or dawn. instead you create class Tv from which all other classes of tv can inherit methods volumeUp() and volumeDown(). thats the power of polymorphism - inheritance. best part is that you can OVERRIDE inherited function if you want that some tv fot example on function volumeUp() do something else - shutdown or something..
happy coding