Beginnger Coefficient of Kinetic Friction Problem

[amd123]

Homework Statement

If you exert 28N of horizontal force while pushing a 10.2 kg box across the surface of a floor at constant velocity, then what is the kinetic friction coefficient between floor and the box?

Homework Equations

EF = ma
Ffk = uK * Fn

The Attempt at a Solution

Fg = 10.2 * -9.8 = -100 = 100 = FN
Ef = ma
28N + Ffk = 10.2 * 0 m/s^2 (constant velocity)
Ffk = -28N

uk = -28/100 = -.28 coefficient is this correct?

 

[Doc Al]

Perfectly correct, except for the minus sign. μN just gives the magnitude of the friction force; μ is always positive.

 

[amd123]

thanks for the help