Two touching bars 1 and 2 are placed on an inclined plane forming an angle α with the horizontal (Fig). The masses of the bars are equal to m1 and m2, and the coefficients of friction between the inclined plane and these bars are equal to k1 and k2 respectively, with k1 > k2. Find:
(a) The force of interaction of the bars in the process of motion;
(b) The minimum value of the angle α at which the bars start sliding down.

2 Fig. 1.10.