Finding the Coefficient of Kinetic Friction Using Acceleration Data

[notdoing]

Homework Statement

Hello. I am working on a physics lab where we pushed a wooden block (weighed at 255.2 g) towards a motion detector. Through this we were able to determine its acceleration.

After five trials we repeated the experiment, but with an additional 500 g weight on top.

From this data I need to find the coefficient of kinetic friction.

Homework Equations

f = (u_k)N = (u_k)mg

The Attempt at a Solution

I know mg, but I don't know the frictional force or u_k. Only one of these have to be known, but I'm not sure how to get there using the acceleration of the block.

 

[notdoing]

since
ma = (u_k)mg

Can I just say:
a = (u_k)g ?