Question

why are the cooking utensils made of copper or aluminium and their handles of hard plastic

Answer 1

the cooking utensils are made up of aluminum and copper because they are good conductors of heat ..
but their hands are made up of plastic and usualy bakelite to prevent our hand from heat
as it can seriously burn our skin

Answer 2

So that they can't react with the acids present in vegetables like oxalic acid in tomato, acetic acid in vinegar. Their handle is of plastic so that person can handle the utensil....