From what little I understand so far, the interceptor was moving in a similar direction to its target (i.e. imagine a car being rear-ended). The debris would mo

From what little I understand so far, the interceptor was moving in a similar direction to its target (i.e. imagine a car being rear-ended). The debris would mostly continue "forward" with a higher velocity than before the collision. Obviously a real impact would be messy and the debris would scatter, but the average velocity of all the remains (including the direction vector) would still need to work out to the sum of the two input vectors. A head-on collision would be a different story, since the overall velocity would be reduced instead.