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-   -   How fast is the dog? (https://www.mersenneforum.org/showthread.php?t=11664)

 Mr. P-1 2009-03-31 15:05

[QUOTE=Andi47;167417]Yes, we assume Newtonian mechanics[/QUOTE]

I would have thought the infinite acceleration stipulated in the question rather foreclosed the applicability of Newtonian mechanics.

 Orgasmic Troll 2009-03-31 15:45

Puzzles like this should be banned, and violators should be woken up by wet-willies for the rest of their life.

The puzzle is set up already violating physical laws, but we're expected to pick out whichever physical law the puzzlemaker arbitrarily decides to keep in. Stupid stupid stupid.

You might as well ask "What color am I thinking of?"

Oughtn't a dog capable of infinite acceleration also be capable of hearing sound transmitted through its body from tail to ears, and, so, hearing the vibrations transmitted thusly from cane to tail through body to ears? What's the speed of sound through dog flesh, skeleton and tendons?

[quote=Orgasmic Troll;167447]The puzzle is set up already violating physical laws, but we're expected to pick out whichever physical law the puzzlemaker arbitrarily decides to keep in.[/quote]Yes, that is an implicit, unstated part of the puzzle, and part of the fun of discussing it.

[quote]You might as well ask "What color am I thinking of?"[/quote]Well ... knowing you ... hmmm ... actually, I don't know you that well, but I can guess anyway ... [spoiler] [I]ultraviolet[/I]. [/spoiler]

Oh, wait -- you're hypothesizing that the [I]reader[/I] is asking someone else, "What color am I thinking of?" Then, the usual answer is [spoiler]"seven" (though a few Doug Adams fans might venture "forty-two")[/spoiler].

 wblipp 2009-03-31 18:16

[QUOTE=cheesehead;167448]Oughtn't a dog capable of infinite acceleration also be capable of hearing sound transmitted through its body from tail to ears, and, so, hearing the vibrations transmitted thusly from cane to tail through body to ears?[/QUOTE]

I worried about that point, too. But I decided that although the dog could hear the cane hitting by this method, the sound would be a thud rather than a clonk much as our own voices sound deeper to us when speaking than on recordings. Hence I concluded the puzzle was carefully worded to avoid this possibility.

 R.D. Silverman 2009-03-31 18:44

[QUOTE=wblipp;167467]I worried about that point, too. But I decided that although the dog could hear the cane hitting by this method, the sound would be a thud rather than a clonk much as our own voices sound deeper to us when speaking than on recordings. Hence I concluded the puzzle was carefully worded to avoid this possibility.[/QUOTE]

Except that whatever the sound IS, it happens [b]behind[/b]
him. Once he is moving faster than Mach 1 he never hears the sound
again.........

 alpertron 2009-03-31 19:36

Well, the sound can pass through the dog's body because the cane is tied to it so the limit is not Mach 1, but at these speeds there are louder noises than the "clonk" the original poster states.

 Uncwilly 2009-03-31 22:45

[QUOTE=wblipp;167426][spoiler]512 m/s.[/spoiler][/QUOTE]
I dispute that, the [B][U]only[/U][/B] assumtion that we are asked to make is the acceleration. Therefore there are two potential answers.

1) [spoiler]~20 m/s, the max speed of any pooch. Greyhounds can burst out to ~45 mph, thus that is the max speed.[/spoiler]
or
2) [spoiler]No speed, because the can not sustain anywhere near that speed over the course of 500km. Therefore, any dog that tries to run that far at top speed will die of exhaustion.[/spoiler]

 alpertron 2009-04-01 01:48

3) [spoiler] The heat generated will rise the temperature of the dog above 100 degrees Celsius, with obvious problems with the water inside the body.[/spoiler]

 retina 2009-04-01 02:35

[QUOTE=Uncwilly;167495]... the [B][U]only[/U][/B] assumtion that we are asked to make is the acceleration.[/QUOTE]Ermm, I think you mean the only physical law we are being asked to suspend is acceleration limits (and maybe inertia and momentum). We are being expected to implicitly assume a multitude of things, like the metre and second being the SI standard, that the dog actually can make such decisions as to run 500km for some unknown reason etc. etc. etc.

I think a more appropriate answer is:

4) [spoiler]The dog never makes to the destination because it gets distracted by hunger, thirst, a rabbit it saw or a bitch in heat. And perhaps multiple of those distractions in succession.[/spoiler]

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