# Barrell poser

glandmaster flash
Posers and Puzzles 20 Dec '08 01:18
1. 20 Dec '08 01:181 edit
Apologies if posted previously.
A freestanding 25kgs barrell is filled with something that immediately makes it weigh just 15 kgs.What has it been filled with to make it lighter than before?
2. Marinkatomb
wotagr8game
20 Dec '08 02:05
Originally posted by glandmaster flash
Apologies if posted previously.
A freestanding 25kgs barrell is filled with something that immediately makes it weigh just 15 kgs.What has it been filled with to make it lighter than before?
helium?
3. 20 Dec '08 03:23
Originally posted by glandmaster flash
Apologies if posted previously.
A freestanding 25kgs barrell is filled with something that immediately makes it weigh just 15 kgs.What has it been filled with to make it lighter than before?
lots of drill holes? ha ha.... just wanted to look at it from a non-scientific angle.ðŸ˜€
4. 20 Dec '08 09:46
Originally posted by Marinkatomb
helium?
Helium might reduce the barrel weight, but not its mass. The barrel must have been filled with some kind of agressive chemical that partly eats away the barrel.
5. 20 Dec '08 10:51
Originally posted by KazetNagorra
Helium might reduce the barrel weight, but not its mass. The barrel must have been filled with some kind of agressive chemical that partly eats away the barrel.
to reduce its weigth immediately? It must be a very agressive chemical.
6. 20 Dec '08 12:22
Originally posted by Thomaster
to reduce its weigth immediately? It must be a very agressive chemical.
Well, you can't instantaneously fill a barrel with helium, either. ðŸ˜‰
7. 20 Dec '08 17:47
Originally posted by glandmaster flash
Apologies if posted previously.
A freestanding 25kgs barrell is filled with something that immediately makes it weigh just 15 kgs.What has it been filled with to make it lighter than before?
Exactly 10kg of antimatter (because 10kg of antimatter will immediately annulated exactly 10kg of matter that makes up the barrel).

-but the problem with that answer is that, by the time the interaction is complete, what is left of the barrel will be immediately vaporised thus you will be left with no barrel.
8. 20 Dec '08 20:32
Originally posted by Andrew Hamilton
Exactly 10kg of antimatter (because 10kg of antimatter will immediately annulated exactly 10kg of matter that makes up the barrel).
Hmm, no, it's not that simple because relativity messes up that balance.
9. 21 Dec '08 05:261 edit
Originally posted by glandmaster flash
A freestanding 25kgs barrell is filled with something that immediately makes it weigh just 15 kgs.What has it been filled with to make it lighter than before?
This is a question that has to be treated scientifically, if it's not just a trick question or joke problem.

A can accept that a barrell can have a mass of 25 kg.
But I cannot accept that this barrel (after the reduction) can weigh 15 kg.

Kilogram is the unit of mass, not of weight.
The unit of weight is Newton, on the other hand, because it is a force.

Do you mean that the barrel has lost a mass of 10 kg? Or is this a part of the joke or trick that mass is converted to a force?
10. 21 Dec '08 11:08
Originally posted by KazetNagorra
Hmm, no, it's not that simple because relativity messes up that balance.
How so?
-I have studied physics at university and I have never heard of this one.
11. 22 Dec '08 14:06
Originally posted by Andrew Hamilton
How so?
-I have studied physics at university and I have never heard of this one.
The mass of elementary particles varies quite a bit, so in antimatter-matter-reactions energy will be converted to mass and mass to energy on quite a large scale. So the final mass of the barrel will depend on what antimatter you're reacting with what matter and what the energy of the antimatter and matter is.
12. 22 Dec '08 20:071 edit
Originally posted by KazetNagorra
The mass of elementary particles varies quite a bit, so in antimatter-matter-reactions energy will be converted to mass and mass to energy on quite a large scale. So the final mass of the barrel will depend on what antimatter you're reacting with what matter and what the energy of the antimatter and matter is.
I am not sure but I think I see what you mean -if a positron meets either a neutron then, despite the fact that the positron has only a fraction of the mass of a neutron, does both all the mass of the positron and ALL the mass of the neutron get converted into energy?

Also, I forgot that, because of the nuclear binding energy is different for each isotope for each chemical element, the number of nucleons an atom has is not exactly proportional to its mass (I am assuming here that all the atoms have their full compliment of electrons and are not ionised). So this would mean that the amount of energy released from, say, 4 hydrogen atoms colliding with 4 anti-hydrogen atoms would be a bit different from amount of energy released from, say, 4 hydrogen atoms colliding with a single anti-helium-4 atom.

Ok -but there is a way around this:

Exactly 10kg of antimatter of a type that is the exact antimatter equivalent of the same type of material the barrel is made of (for example, if the barrel is made of pure iron-52 isotope then the antimatter must be pure anti-iron-52 isotope) will annulated almost exactly 10kg of the mass of the barrel (although you will still be left with no barrel).
13. 23 Dec '08 14:35
The simplest interaction between a neutron and a positron I can think of is the conversion of a neutron into a proton through exchange of a W+ boson, not sure how much mass is converted in that reaction. This is simply the inverse of positron beta decay.

e+ + electronneutrino + n -> p
14. 23 Dec '08 22:31
If its a trick question ..is it freestanding on a scale with -10 kg tare weight so it would always weigh 15 kg
15. 24 Dec '08 16:34
Originally posted by glandmaster flash
Apologies if posted previously.
A freestanding 25kgs barrell is filled with something that immediately makes it weigh just 15 kgs.What has it been filled with to make it lighter than before?
Please tell us what the answer is -I think we give up.