163. A 2\,kg mass is attached to the end of a spring of length 30\,cm and we hang it; the spring stretches to 42\,cm. Now we attach another weight equal to this weight to the same spring and move it on a horizontal surface with acceleration $2\,\dfrac{\text{m}}{\text{s}^2}$. If in this case the length of the spring reaches 36\,cm, the coefficient of kinetic friction of the body with the horizontal surface is how much? $\left(g = 10\,\dfrac{\text{m}}{\text{s}^2}\right)$
(1) $0/2$ (2) $0/3$ (3) $0/4$ (4) $0/5$