Falling Object – State-space and “measure” position

Have the following equation: ma(t)= m(-g) – f*v(t).

Sum of forces on object consists of gravity*mass and a constant f proportional to the velocity of the falling object.

How do I set this up as a state-space model? Matrices A, B, C & D.

I’ve tried the following, but I must be doing something wrong:

A=[0,1;0,-f/m], B=[0;-g], C=[1,0], D=[0]