relative motion-1

[phyti]

SR states that time dilation and length contraction depend on the relative
velocity of the reference frames.
B moves at .6 c relative to A.
B sees objects of known dimensions passing in the opposite direction appearing contracted to .8 their length.
A accelerates to .2 c in the direction opposite of B.
The relative speed of separation is now approximately .8 c.
This would require the contraction to be approximately .6 c.
The objects moving past B do not speed up when A moves.
What's wrong with this picture?

[HallsofIvy]

SR states that time dilation and length contraction depend on the relative
velocity of the reference frames.
B moves at .6 c relative to A.
B sees objects of known dimensions passing in the opposite direction appearing contracted to .8 their length.
A accelerates to .2 c in the direction opposite of B.
Relative to what? If it is relative to B's frame of reference then the original ".6c" is irrelevant and A does NOT now have speed 0.6c+ 0.2c= 0.8 c relative to B, he has speed 0.2 relative to B just as you said. It cannot be relative to A's original frame, that frame no longer exists.

The relative speed of separation is now approximately .8 c.
This would require the contraction to be approximately .6 c.
The objects moving past B do not speed up when A moves.
What's wrong with this picture?
Again, relative to what? This makes no sense unless you specify what frame of reference is being used at each step.