The force of static friction acting on the box is approximately

To find the force of static friction acting on the box, we'll need to consider the forces acting along the incline of the ramp.
First, let's determine the component of the gravitational force parallel to the ramp's surface. This force, known as the component of the weight force along the incline
, can be calculated using trigonometry:
![\[ F_{\text{parallel}} = F_{\text{gravity}} * \sin(\text{angle of incline}) \]](https://img.qammunity.org/2024/formulas/physics/high-school/3uxg9kg6hzmbdx9xc02ox3fid08ilyplsy.png)
Given that the gravitational force
is 112.1 N and the angle of incline is 42°:
![\[ F_{\text{parallel}} = 112.1 * \sin(42^\circ) \]](https://img.qammunity.org/2024/formulas/physics/high-school/booieqloi9tkkdpgdayy3c421b7uhrzgxo.png)
Let's calculate

![\[ F_{\text{parallel}} \approx 112.1 * 0.669 \approx 75 \, \text{N} \]](https://img.qammunity.org/2024/formulas/physics/high-school/qc3dbv317m2pxin3hh3oj2bmw2o2tc9lbd.png)
Now, since the box is at rest and in equilibrium halfway up the ramp, the force of static friction
must be equal in magnitude and opposite in direction to
to prevent the box from sliding down or up the ramp.