Any questions?? Ask/answer questions below in the discussion thread.
It is recommended that you use the moving reference frame kinematics equations relating the motions of A and B:
vA = vB + (vA/B)rel + ω x rA/B
aA = aB + (aA/B)rel + α x rA/B + 2ω x (vA/B)rel + ω x (ω x rA/B)
Placing the observer on bar ACD prescribes ω and α to be the (unknown) angular velocity and angular acceleration, respectively, of ACD. What do you use for the relative velocity and relative acceleration terms, (vA/B)rel and (aA/B)rel ? The observer on ACD sees B moving along the slot. The magnitudes of these relative velocity and acceleration terms are unknowns, however, the two vectors are aligned with the slot.
In order to determine the velocity and acceleration of B for the above equations, you will also need the rigid body kinematics equations relating the motions of O and B:
vB = vO + ωBO x rB/O
aB = aO + αBO x rB/O + ωBO x (ωBO x rB/O)