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1. Why is it difficult to hold a school bag having a strap made of a thin and strong string?
Answer :

It is difficult to hold a school bag having a strap made of a thin and strong string because of the pressure exerted by straps on shoulder. As the smaller is the surface area the larger are going to be the pressure on the surface. Within the case of a thin strap, the contact is tiny. Hence, the pressure exerted on the shoulder is large.