A man holds a book vertically between his two palms so that it does not fall. The mass of book is 1 kg and the force exerted by each palm is `2.5 kg xxg`. Find the coefficient of friction between the book and the palm.

Explanation

Weight of the book is 1 `kgxxg` which acts vertically downwards . As two surfaces of the book are pressed by two hands downward force on each surface of the book = `(1kg xxg)/(2) = 0.5kg xx g`.
As the book is at rest the frictional force acts upwards to balance this downward force of `0.5kgxxg` on each surface. So the limiting force of friction, f = `0.5kgxxg.`
Force exerted by each hand = normal force ( R) = `2.5kgxxg`
`:.` Coefficient of friction,
`mu = (f)/( R) = (0.5 kg xxg)/(2.5 kg xx g)` = 0.2.