An elastic rod of length l , flying with speed v, collides with the end of a fixed
1
rod of length l , l1 > l2 , where c and c are sound speeds in one and the
2 c1 c2 1 2
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other rod respectively. The cross-section of the rods and the density of their
material are the same. Determine the velocity of the centers of mass of the
rods after the collision.