The fact that the woman falls at a constant velocity means its acceleration is zero.
For Newton's second law, the resultant of the forces acting on a body is equal to the product between the mass m of the body and its acceleration a:
[tex]\sum F = ma[/tex]
In our problem, the acceleration is zero, so the resultant of the forces should be zero as well.
Only two forces are acting on the woman: the air resistance R (upward, 500 N) and the weight W (downward). The resultant of these two forces is zero, so
[tex]R-W=0[/tex]
[tex]W=R[/tex]
and since the air resistance R is 500 N, then the weight (the gravitational force) of the woman is 500 N as well.
