Questions and discussion for this lecture live here. Fire away by hitting Reply below 
Hello
first of all, thank you so much for the lessons and the explanations. I have a question though:
I tried to solve the problem before watching the video and for that I used the A and B equations whose solutions we found on lesson 22. These are the formulas I used:
C = xi * (4 * m * k)0.5
A = (-P * (k - m * omega2))/((-(C * omega)2)-((k - m * omega2)**2))
B = (P * C * omega) / ((-(C * omega)2)-((k - m * omega2)**2))
I thought that would make sense since we didn’t have any boundary conditions there and thus, it would be the general solution for every problem. I was further encouraged as I saw that the graphic you obtained in the video and the one I got seem to be exactly the same.
However, I checked the numbers and they’re not the same: in t=11, I get
0.0014773545483487552 m
and you get:
0.004512732017151165 m
I didn’t introduce any velocity boundary contition, so I’m pretty sure my solution is wrong. My question is: what did I calculate with my result?
Ah…I see where the confusion arises…and it’s completely my fault!!
Back in lesson 22, the constants A and B that appear in equations (2) to (10) are local or specific to the determination of the particular solution. You’ll see from equations (9) and (10) that they depend only on system constants and are not time dependent.
However, the terms A and B that appear as part of the complementary solution in equation (13) are in fact different constants…that depend on the system initial conditions…as demonstrated in this lecture (26). I should have used different symbols or made this clearer…apologies!
Let me know if you still have questions.
Seán
Oh I see it now. Thank you very much for your expalantion!