What speed would a bag containing an average sized faeces have to be
travelling, in open space, to be capable of cleanly removing a human
head ( including space helmet)?

ehhgh..............

like a flee hitting a large rock. i hate people.

The energy of the cohesive force holding the system together at the
neck is E. So you'll need an impact of energy > E, to guarantee both
severance and separation.

   Kinetic energy is E    = mv^2/2. 

                    2E    = mv^2
                    2E/m  =  v^2
               sqrt(2E/m) =  v

   So the speed of your crap must be greater than v. My guess is
you'll have no problem if you eat a high fiber diet.

cheers for the input qed100, but i'm looking for actual figures, need
to get my moneys worth you know. Can't the average wieght of a dump be
found on the net? You forgot 2 take into account the helmet.

eliteskillsdotcom since the shit would be frozedn solid in space i
think it would have a little more impact than " a flee hitting a large
rock " u twat. Just so you know, people hate you too

Hi,

   The problem isn't the mass of a lump of poop. It's finding data on
the shear/tensile strength of a typical human neck. Also the space
helmet will depend on what suit design one is considering; there are
and have been a number of them.

   Incidentally, I didn't exactly neglect the helmet in my
(admittedly) meaningless) calculation; I simply called everything the
"system". :)

Well, one of my average logs is probably 0.5 lb.  And then the little
rabbit-turds that follow are probably 0.1 lb...  (I hate those little
guys...)

However, a large portion of the mass comes from water.  In space, the
water would be gone, right?  Wouldn't it turn to ice immediately and
then sublime into gas?  I may be wrong... ANYWAY, I'm guessing your
log would lose about 50% or 60% of it's mass when it instantly dries
out and freezes.

Then, you have to decide whether to assume the log slowly dropped out
of 'Uranus', or whether it was something like explosive diarhea, where
the speed could be more like 10-20 mph.  Either way, those speeds are
pretty slow.

For a 0.25 lb loaf, I'm guessing it would have to travel somewhere
around 750 - 1000 mph in order to sever the head and helmet...