Question

why it is easier to cut an apple with a sharp knife

Answer 1

It is easier to cut from a sharp knife as the surface area of sharp edges get decreased and all pressure by you is exerted at a particular point .
smaller the area more the pressure ,
greater the area less the pressure

Answer 2

The sharp edge of knife has a smaller area and the pressure is inversely proportional to area of contact. so it exert a greater pressure on the Apple and cut easily