Question

why is it difficult to hold a school bag having a strap made of thin and strong sting​

Answer 1

Because when area decreaces pressure increases. So the school bags which have thin and strong stings are difficult to carry but bags having thick straps are easy to carry as when area increases pressure decreses

Answer 2

Your question :- Why it is difficult to hold a school bag having strap made of thin and strong string

Answer. :-

It is difficult to hold a bag which have thin and strong string as

Because of its thinnes it have less surface area in contact with our shoulder , hence maximum amount of force is applied at a single place which makes it difficult to hold

And as it is strong , It will not break easily to relax our shoulders """.

Hope it helps