In reply to Newbie-in-London:
> Thanks oldie, so it would be safe to fall from 5m on a new rope? <
Yes, if you fell with no runners (ie factor 2) from 5m above your belayer the length of fall would be 5m from above + 5m below your belayer +1.25 m if the rope stretched 25% ie 11.25m (if my maths is correct!). Leaving you about 6.25m below the belayer.
However it is always far better to start placing runners as soon as possible since this reduces the fall factor and thus the impact force on both you and your belayer and it is easier for them to arrest your fall, I'm sure you will know this from your course.
The force will actually be further reduced, for example by some rope run through many belay devices, and you will be cushioned by your harness,
After a severe fall the part of the rope involved will take some time to regain full elasticity (although they are certified to hold several such falls).
Post edited at 22:30