Solving for Friction Coefficient: 105N & 3.00 m/s^2

[dorkee]

Homework Statement

A force of 105N is applied horizontally to a 20.0 kg box to move it across a horizontal floor. If the box has an acceleration of 3.00 m/s^2, find the coefficient friction.

Homework Equations

coefficient friction = Ff/Fn

The Attempt at a Solution

I converted the mass into Newtons so 20.0 kg = 196 N
I have no idea how to do this. I drew a picture, but I don't know what to do with the acceleration.

 

[LowlyPion]

Homework Statement

A force of 105N is applied horizontally to a 20.0 kg box to move it across a horizontal floor. If the box has an acceleration of 3.00 m/s^2, find the coefficient friction.

Homework Equations

coefficient friction = Ff/Fn

The Attempt at a Solution

I converted the mass into Newtons so 20.0 kg = 196 N
I have no idea how to do this. I drew a picture, but I don't know what to do with the acceleration.

Ok. What would the acceleration be if there was no friction?

Won't the difference then be how much friction has retarded its motion?