Tumin's conclusion refers to the boundary conditions taken in the form Q2-Q1=0. For the solution of our problems the boundary conditions in the form Q2=Q1=C should be used, where constant C may be different on the perturbed and nonperturbed shock surfaces. The difference in C values proceeds from the potential of applied force, resulting in the nonstationary (accelerated) motion of a shock surface. In the noninertial reference frame associated with the perturbed shock surface, the inertia force causes acceleration. The physical reason for its appearance is the force of internal friction inside the viscous front of a shock wave.