The box in the above picture is falling from the top of a building to the ground. two major forces are acting on the box as it falls. which force is represented by the arrow labeled q?

  Q= Air resistance

Description:

The box release two forces acts on it, when it is falling from the building.

1. Its weight,  2. Air resistance

As this point its weight is much greater due to the force of gravity on the objects, so it accelerates downwards. As its speed increases so does the drag on the object so its acceleration starts slow down until it reaches to zero.  At which point air resistance will be equal to weight of the object leaving a resultant force of zero.