Question

Anna applies a force of 19.5 newtons to push a book placed on a table. If the normal force of the book is 51.7 newtons, what is the coefficient of kinetic friction?

Answer 1

Considering that the book is moving with constant speed, the force applied by Anna must be the same that the friction force:

$F = F_R = F\cdot \mu_k\cdot N$

If we clear the previous equation:

$\mu_k = \frac{F}{F_R} = \frac{19.5\ N}{51.7\ N} = \bf 0.38$

Answer 2

The force applied to the book is equal to the normal force of the book multiplied by the coefficient of kinetic friction. The normal force is equal to the weight of the book. In this case, the formula with the given data is equal to 19.5N = 51.7N * coeff. of friction. The coefficient of friction is equal to 0.38.