A problem of pulleys

Hi,

First, is there a simple way to write the double derivative of a function say x(t) so I will receive as output x(t) with the double quote on the top instead on writing it in a long form diff(x(t),t,t)

Secondly, I have a problem with a system of pulleys.  See if you can find where I am missing something.  Here the file:

View 3867_poulie3.mw on MapleNet or Download 3867_poulie3.mw
View file details

Thanks in advance

Mario