A girl pushes a 1.04 kg book across a table with a horizontal applied force 10 points
of 15.0 N. If the coefficient of kinetic friction between the book and the
table is 0.35, find its acceleration. *​

Respuesta :

Answer:

Approximately [tex]11.0\; \rm m \cdot s^{-1}[/tex]. (Assuming that [tex]g = 9.81 \; \rm N \cdot kg^{-1}[/tex], and that the tabletop is level.)

Explanation:

Weight of the book:

[tex]W = m \cdot g = 1.04 \; \rm kg \times 9.81\; \rm N \cdot kg^{-1} \approx 10.202\; \rm N[/tex].

If the tabletop is level, the normal force on the book will be equal (in magnitude) to weight of the book. Hence, [tex]F(\text{normal force}) \approx 10.202\; \rm N[/tex].

As a side note, the [tex]F_N[/tex] and [tex]W[/tex] on this book are not equal- these two forces are equal in size but point in the opposite directions.

When the book is moving, the friction [tex]F(\text{kinetic friction})[/tex] on it will be equal to

  • [tex]\mu_{\rm k}[/tex], the coefficient of kinetic friction, times
  • [tex]F(\text{normal force})[/tex], the normal force that's acting on it.

That is:

[tex]\begin{aligned}& F(\text{kinetic friction}) \\ &= \mu_{\rm k}\cdot F(\text{normal force})\\ &\approx 0.35 \times 10.202\; \rm N \approx 3.5708\; \rm N\end{aligned}[/tex].

Friction acts in the opposite direction of the object's motion. The friction here should act in the opposite direction of that [tex]15.0\; \rm N[/tex] applied force. The net force on the book shall be:

[tex]\begin{aligned}& F(\text{net force}) \\ &= 15.0 \; \rm N - F(\text{kinetic friction}) \\& \approx 15.0 - 3.5708\; \rm N \approx 11.429\; \rm N\end{aligned}[/tex].

Apply Newton's Second Law to find the acceleration of this book:

[tex]\displaystyle a = \frac{F(\text{net force})}{m} \approx \frac{11.429\; \rm N}{1.04\; \rm kg} \approx 11.0\; \rm m \cdot s^{-2}[/tex].