Do you understand
There is a simple and often using lab on measuring of the coefficient
of the kinetic friction (in this situation we are talking about the coefficient
of the friction between the surface and the block m).
To do this we can place a wooden
brick of mass m on a horizontal surface, put on it an additional weight
of mass M, hook up the spring scale to the brick and pull it up with the constant speed.
After measuring the applied pulling force F we can
find the coefficient of the kinetic friction between the surface and the block
m as
μ = F/g(m+M)
Now, the question is:
Draw the free-body diagram and write the second