Hey
So I followed similar approach to yours and I believe we get the same answer
my approach:
assumption 1: Argon is an ideal gas
mAB = mB (COM)
1st law:
E2- E1 =Q -W
since it is well insulated Q = 0 (Adiabatic)
and because it is rigid body I assumed there is boundary work so W = 0
From...