Answer to Question #162082 in Physics for Janine

Question

A girl is pressing a 2-kg book against a vertical wall. If the coefficient of friction between the book and the wall is 0.30, how hard should the girl push to allow the book to slide down the wall at a constant speed?

Answer 1

Let's apply the Newton's Second Law of Motion:

$$\sum F_y=ma_y=0,$$ $$F_{fr}-mg=0,$$ $$\mu N-mg=0,$$ $$\mu F-mg=0,$$ $$F=\dfrac{mg}{\mu}=\dfrac{2\ kg\cdot9.8\ \dfrac{m}{s^2}}{0.30}=65.3\ N.$$