Ships dont telescope in the same way a train does, they arent small units joined together by flexible couplings.
I have seen simulation results that showed a head on collision would have resulted in catastrophic hull failures along the length of the hull, with sinking occuring quite rapidly.
I am new here - forgive my jumping into the "deep" end, but this is an area of interest for me. Some related and semi-related trivia...
Despite the clear picture painted of events on that night, there are a lot of things that were viewed for a long time as fact that are somewhat questionable.
(1) There is no data, believe it or not, of water overtopping the bulkheads. Flooding appears to have come from damage below, and from bulkheads giving way.
(2) Helm and engine orders have a very murky path to us through history. One thing is clear though - the engines were more than likely never reversed. The reversal process required a large number of people to all be in the right places - which was not true late at night in mid-ocean - in perfect conditions, reversal took a couple of minutes. Engine orders after the collision are even murkier.
(3) The whole timeline of the collision is still bitterly debated among historians.
There are some superb historians over at the Encyclopedia Titanica website - I encourage the curious to check it out.
Wayne
The boilers & engines would strain their mountings, probably, even break 'em, but they probably wouldn't "lurch forward". They'd be designed to withstand grounding (more/less the same kind of shock), which would be expected due to (for instance) unexpected sandbars, mistaken charts, or bad piloting (distinct from this situation, bad Master's decision... Honestly, running at full speed, at night, in known iceberg waters?but imagine the impact on the mountings holding these in place as they lurch forward, possibly smashing bulkheads.
Then you've got whatever heavy cargo isn't secured to withstand lurching fore and aft in a very violent manner.