Solving for Coefficient of Friction with 30N Force

[glindawantsme]

Homework Statement

If you use a horizontal force of 30.0N to slide a 12.0-kg wooden crate across a floor at a constant velocity, what is the coefficient of kinetic friction between the crate and the floor?

Homework Equations

F_f=$$\mu$$_kF_N

The Attempt at a Solution

I thought maybe it would be 30.0N=$$\mu$$_k(12.0kg)(9.8m/s²90, but I don't know if that's right. Is 30N the force of friction? Please help me!

 

[Doc Al]

You are doing fine. Yes, the 30N force = force of friction. (Since the box moves with constant velocity, what must be the net force on it? That's what should convince you that the applied force and the friction must be equal and opposite.)