help needed - Shock absorber experiment

Im doing a little experiment o investigate how shock absorbers work and im having a little trouble with what to do with the results.

To model the shock absorber im using a tube with a plunger in it and 1/2 litre of glycerol as the fluid. I have then used some pulley and put varied masses (o.1kg to 0.6kg) on the end of the string to pull the plunger up. I’ve timed the movement of the plunger over a set distance with different masses.

Now for my graph work i think i need to plot drag force against the velocity. Now i know how to calculate the average velocity but i think i need the constant velocity of the plunger when under different forces. Acceleration must be 0 so the drag force would equal the mg but i have no idea how to use this data to calculate the constant velocity.

I thought i may need to the record the times for the plunger to move small increments over the larger distance and then plot this in a table which using the s=vt i would see where the velocity is constant and a value for this.

any help much appreciated

Steve