Answer
As $F_{2}$ increases, the magnitude of the static friction increases.
Work Step by Step
To move an object along a rough surface, the force moving the object must over come the force of static friction between the box and the ground. An object of greater mass will created a greater static friction force. In this situation, $F_{2}$ is acting like a greater mass. So as $F_{2}$ is increased, the magnitude of static friction increases.
