Copyright © University of Cambridge. All rights reserved.
'Moving Stonehenge' printed from https://nrich.maths.org/
Archimedes' Principle says that when you displace some volume of
fluid, you experience an upward force equal to the weight of the
fluid displaced.
The problem boils down to finding out how much weight a
metre of log can support.
Many physics A-Level syllabuses cover Archimedes' Principle, which
is covered in more depth in most 1st year general engineering
courses.