Question

why is it difficult to cut the vegetable with the blunt knife

Answer 1

because the blunt knife is not much strong than a knife

Answer 2

Hi there !!

It is difficult to cut the vegetable with a blunt knife . This is because of the area of contact.

We know that force is inversely proportional to area of contact. This means that if the area of contact is decrease, the force will increase and vice versa.
Since blunt knives have a wider and a larger area of contact, the pressure exerted on the vegetable is comparitively less than that of a sharp knife.
So, it is difficult to cut the vegetable with a blunt knife.