Question

when you place a book above your head how many force pairs act on the book?
a.1
b.2
c.3
d.4
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Answer 1

When you place a book over your head, a. 1 force pairs act on the book.

When a book is placed on head, it is in equilibrium. Hence, sum of the total forces acting on the book is zero.

Gravitational force acts on the book in downwards direction.

As per Newton's third law of motion, equal and opposite reaction acts for every action.

To balance the gravitational force, normal reaction acts on the book in upward direction.

Thus, a pair of forces gravitational and normal reaction are acting on the book.