What is the coefficient of kinetic friction between the object and the floor?

Question

An object slides on a level surface in the +x direction. It slows and comes to a stop with a constant acceleration of -2.45 m/s^2. What is the coefficient of kinetic friction between the object and the floor?

Answer 1

The coefficient of kinetic friction μ is defined as the ratio of the friction force F to the normal force N:

μ = F/N

The normal force is the reaction by the plane to to the weight mg of the object.

The friction force has the magnitude ma

Therefore μ = ma / mg = a / g = 2.45 / 9 = 0.27

Answer 2

µ = a/g = 2.45/9.8 = .25