If one object is sliding on the surface (i.e. it is in motion relative to the other one ) then there is a force of kinetic friction between the two objects. the direction of this force opposes the sliding motion and its magnitude can be calculated by:
N= normal force between the two objects and
μk=the coefficient of kinetic friction for the two surfaces.
from our description above we can be able to derive the equation
20=μk X 10
and thus the coefficient of the kinetic friction for the two surfaces will be 2