Minimum force to pull a sled at constant speed

[tutojean]

Homework Statement

A sled is pulled at a constant speed over a horizontal surface where the kinetic coefficient of friction is .20. What is the minimum force necessary to keep the sled moving if its mass is 2 slugs?

Homework Equations

f(s)=U(s)N or f(s)=Ns(mg)

F(s)= Frictional Force
m=weight
g=gravity
(Not sure about this equation or problem)

The Attempt at a Solution

F(s) = Ns(mg)
F(s) = (.20)(2 slugs)(32 ft/s^(2))
F(s) = 12.8 N ?

Am I doing this right or wrong? Can somebody please show me how to do this?

 

[Redbelly98]

You did it right, except that the force units are not Newtons.

What force units go with feet, slugs, and seconds?