| Physics riddle | |
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JavaGuy - Student  |
Two barrels of water, one frozen solid and the other at room temperature, start rolling at the same time from the same height on a ramp. Both are the exact same mass. Which one reaches the bottom first and why? _______________ My signature is only one line. You're welcome. |
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Daidalus[JAP] Fisto - Student ![Daidalus[JAP] Fisto](/image_thumbnail.php?f_type=users&f_width=49&f_height=70&f_image=3482.jpg){kind=small}
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for those,who dont beleave thats very simple, try this: take a raw egg and a hard cooked egg. Than you turn them arund on the table. The uncooked one will slow down very fast, but the cooked one will turn further. Its the same principe like the barrels, the solid one turns faster, thats why its the first. But there is one more aspect: it doesnt matter if the mass is exactly the same. if there are two barrels, one full of solid iron and one full of solid ice. They will have excectly the same speed. Thats what Newtonproofed whis his princips of gravitation.  But i dont know how the mass of the liquid water influences the speed of the barrel... if there is too less whater in it, there is nothing left that can slow down the barrel...  greetings, daid _______________ Founder of the Fisto Family -|- Member of the mighty FiZZsters!! -|- Owner of the second Bail prize for "BAIL RULES!!" -|- I'll never forget you Jaina! -|- Owner of the one and only autograph of Smily -|- SMILY RULES  -|- Owner of the 1000th Comment of the great Kueller -|- Big brother to NarCosT Fisto, and ShadowFax . -|- Proud Padawan of Kueller -|-Sir Daidalus Fisto. Official Historian of Nippledom and server to Menaxia, Queen of Nippledom Quote: fiZZe: "gdamubububugmgmgububugrrrrrdsa?"
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Casual - Student 
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After reading this whole thread, I conclude more strongly then ever that I truly need a beer (and I presume most of you others too) Bah, science. I'm all for the optional hippy-studies instead of figuring out some insertia or something. But it's great that someone is interested in Newton and his misunderstood friends. -Cas PS: Omg, I think I'm slowly mastering the art of useless posting _______________ Thanks to the human heart by which we live, Thanks to its tenderness, its joys, and fears, To me the meanest flower that blows can give Thoughts that do often lie too deep for tears. |
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Ancient - Ex-Student 
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Quote: Um, I did say it was a physics riddle, by which I meant it involved basic physics. And no, I didn't take offense at anything anyone said. Ancient and I did give long-winded explanations of the answer for the benefit of those who haven't studied physics but might be interested, but to any beginning physics student the answer "the water barrel because it has a different moment of inertia" is all the answer he needs. I took the time to explain what that means because I thought non-science geeks might nonetheless want to know why. To be sure: The answer to this requires nothing beyond what you learn in introductory physics. I figured it out in a heartbeat when I was a young pup, and yet over the years I have presented it to no fewer than three people who had Masters Degrees in Physics, and only one of them got it. So it seems to me that it is indeed a riddle in the classical sense of the term, but yes, it's a physics riddle--it does require some basic knowledge of physics, but discovering the answer is more a matter of inspiration than of specialized knowledge. If it were a physics test question I'd have given the mass of the ice barrel, the height of the ramp and asked its speed when it reached the bottom.  If I post any more like this I'll be sure to indicate what, if any, prerequisit knowledge it takes. Well said. PS plz post more of those..../me interested _______________ -THE ONE WITH THE "STAFF" -BROTHER TO FROSTY -Admitted to University of California, San Diego(UCSD). YAY! |
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JavaGuy - Student 
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Um, I did say it was a physics riddle, by which I meant it involved basic physics. And no, I didn't take offense at anything anyone said. Ancient and I did give long-winded explanations of the answer for the benefit of those who haven't studied physics but might be interested, but to any beginning physics student the answer "the water barrel because it has a different moment of inertia" is all the answer he needs. I took the time to explain what that means because I thought non-science geeks might nonetheless want to know why. To be sure: The answer to this requires nothing beyond what you learn in introductory physics. I figured it out in a heartbeat when I was a young pup, and yet over the years I have presented it to no fewer than three people who had Masters Degrees in Physics, and only one of them got it. So it seems to me that it is indeed a riddle in the classical sense of the term, but yes, it's a physics riddle--it does require some basic knowledge of physics, but discovering the answer is more a matter of inspiration than of specialized knowledge. If it were a physics test question I'd have given the mass of the ice barrel, the height of the ramp and asked its speed when it reached the bottom. If I post any more like this I'll be sure to indicate what, if any, prerequisit knowledge it takes. _______________ My signature is only one line. You're welcome. |
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Ancient - Ex-Student
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Quote: I riddle has a simple answer to a seemingly complex question. This has both a complex question and a complex answer. This question is complex? You are just kidding me, look at any physics book dude.... A complex answer? Of course not, this question has only one answer: 1/2 chance, and the explanation is not hard to understand either, which only involve two principle of physics. P.S. this is the explaination for riddle from the US dictationary riddle AHD:[r¹d“l] D.J.:[6ridl] K.K.:[6r!dl] n. A question or statement requiring thought to answer or understand; a conundrum. One that is perplexing; an enigma. I think you misunderstood the true meaning or "riddle" _______________ -THE ONE WITH THE "STAFF" -BROTHER TO FROSTY -Admitted to University of California, San Diego(UCSD). YAY! This comment was edited by Ancient on Apr 23 2004 02:18am. |
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Fizz of Belouve - Student 
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the frozen one, coz its solid, and there is no friction inside. _______________ One of the Belouve boys, founder of the mighty FiZZsters Midbie council #20 - Fizz - #1933 - Jan '03 - Aug '04 "Renfield, you idiot!" |
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Gradius - Ex-Student 
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Thank you Obi. _______________ - Proud padawan of Kueller. - We really are at the beginning of it all. The trick, of course, is to make sure we never find the end. - Bill Bryson, A Short History of Nearly Everything - <gen-e-sis-happy> Liek, you can train, liek, a n00b, but he'll just be a trained n00b... --> Wise words! - "daer SOE me likes your a company i am having your some money for letting me do stuff cos mes the best amd i do it all meself" - Slider |
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(Jedi)Obi-JK - Student 
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I wouldn't consider this a riddle, I would call it a question or problem. A riddle, to me is a question that requires thought to answer but only common sense, or general knowldge. This question / problem, requires thought but is more bassed on ones knowledge of phyics. _______________ Silent Bob (Kevin Smith): You know, there's a million fine looking women in the world, dude. But they don't all bring you lasagna at work. Most of 'em just cheat on you. -Steve (Obi) |
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Gradius - Ex-Student
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Whoa man first off I'm not taking anything out on anybody. Second, it's not a riddle. It's a basic physics exam question. I riddle has a simple answer to a seemingly complex question. This has both a complex question and a complex answer. Nothing about it makes it a riddle except for the fact JavaGuy held out on the answer (which is good). I appologize for sounding mad or anything, I'm not. Just a little disappointed is all. I never took any physics class so to me it was just a "game" sort of speak. Sorry. _______________ - Proud padawan of Kueller. - We really are at the beginning of it all. The trick, of course, is to make sure we never find the end. - Bill Bryson, A Short History of Nearly Everything - <gen-e-sis-happy> Liek, you can train, liek, a n00b, but he'll just be a trained n00b... --> Wise words! - "daer SOE me likes your a company i am having your some money for letting me do stuff cos mes the best amd i do it all meself" - Slider |
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Bubu - Hubbub 
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The title says "Physics Riddle", implying you have to use principles of physics. Knight, You are at fault here for expecting something that was never promised to you in the first place. JavaGuy did nothing wrong, don't take it out on him. _______________ make install -not war This comment was edited by Bubu on Apr 22 2004 08:42pm. |
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JavaGuy - Student 
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How is that not a riddle? _______________ My signature is only one line. You're welcome. |
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Gradius - Ex-Student 
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Dude that is not a riddle. I appologize for saying you don't have to think that far into this one because this has no trick answer to it. Thanks for getting my hopes up JavaGuy.  _______________ - Proud padawan of Kueller. - We really are at the beginning of it all. The trick, of course, is to make sure we never find the end. - Bill Bryson, A Short History of Nearly Everything - <gen-e-sis-happy> Liek, you can train, liek, a n00b, but he'll just be a trained n00b... --> Wise words! - "daer SOE me likes your a company i am having your some money for letting me do stuff cos mes the best amd i do it all meself" - Slider |
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JavaGuy - Student
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Ancient...I thought you said the ice barrel would reach the bottom first. Anyway, Ancient hit on the correct principle: Moment of inertia (one-half eye omega-squared). The thing to remember is that both barrels have the exact same potential energy at the top because they have the same mass and start from the same height. As they roll to the bottom, potential energy is converted to kinetic energy. Because of the law of conservation of energy, if they had the same potential energy at the top, then they have the same potential energy at the bottom. So if they have the same potential energy at the bottom, they're going the same speed? No. Each barrel has two kinds of kinetic energy when it reaches the bottom, energy of translation and energy of rotation. Energy of translation is the energy of the whole barrel moving from one place to another. Energy of rotation is the energy of the barrel spinning around. If a barrel is flying through space and not turning, it has energy of translation but none of rotation. If a barrel is spinning in one place, it has energy of rotation but none of translation. If it is rolling down a ramp, it has a little of both, and the total of its energy of translation plus energy of rotation as it hits bottom has to be exactly equal to the potential engery (1/2mgh) that it had at the top of the ramp. To understand energy of rotation, think about an individual molecule inside the frozen barrel (it could be a molecule of water or a molecule of iron in the barrel itself). If the barrel makes one rotation per second, then that molecule is moving in a circle around the axis of the barrel at a speed of that circle's diamater per second. The individual molecule's kinetic energy is one-half its mass times the square of its velocity. Molecules close to the center travel around a smaller circle in the same amount of time and so move slower, have less energy. Molecules around the rim move the fastest and have the most energy. The barrel's total energy of rotation is the sum total of every molecule's kinetic energy with respect to its motion around the axis. Now when the ice barrel starts to roll, the ice, being solid, must roll exactly as fast as the barrel. The amount of energy that goes into rotational motion to achieve a given translational speed down the ramp is fixed. But when the water barrel starts to roll, inertia will cause the water to lag behind the barrel in rotational speed. Friction will cause the water to rotate, but it won't rotate as fast as the outside of the barrel, at least not when it first starts out, and thus it will require less energy to get it rolling the same speed as the frozen one. Since they both start out with the same potential energy, the water barrel will start rolling faster. _______________ My signature is only one line. You're welcome. |
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Gradius - Ex-Student
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Man that's not what I mean I know why we need science. What I mean is that this is a RIDDLE, a JOKE, a GAME. It doesn't require this much thinking into. It's an answer of common sense. JavaGuy wasn't asking us out of his own curiosity. That's what I mean when I say you guys are thinking too far into this. It's a simple question with a simple answer that you don't really have to do math to figure out. _______________ - Proud padawan of Kueller. - We really are at the beginning of it all. The trick, of course, is to make sure we never find the end. - Bill Bryson, A Short History of Nearly Everything - <gen-e-sis-happy> Liek, you can train, liek, a n00b, but he'll just be a trained n00b... --> Wise words! - "daer SOE me likes your a company i am having your some money for letting me do stuff cos mes the best amd i do it all meself" - Slider |
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Ancient - Ex-Student
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Quote: JavaGuy just tell us the answer please. Everyone's getting in way too deep with all this physics talk and they don't understand it's a very simple answer. Im sticking with mine still. The water barrel will reach bottom first because the ice barrel will get a slower start rolling. First, you have to understand that human intuition is not accurate at all, thats why we need science, we need laws to prove our hypothisis. If everyone prove and conclude things will there instinct, you wont be sitting in a chair that is that comfortable, you wont be sleeping in your bed without fear that it will collapse, you cannot ride any car or bus to school that safe, and you will never see any airplane in your life time, etc. You can see science everwhere, from small things to big things. They are all science and hypothesis that have been proven. Hope that change you view point.P.S. if we all dont know what is density, everyone will think that ice will have a smaller mass than water _______________ -THE ONE WITH THE "STAFF" -BROTHER TO FROSTY -Admitted to University of California, San Diego(UCSD). YAY! This comment was edited by Ancient on Apr 22 2004 05:34pm. |
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Gradius - Ex-Student
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JavaGuy just tell us the answer please. Everyone's getting in way too deep with all this physics talk and they don't understand it's a very simple answer. Im sticking with mine still. The water barrel will reach bottom first because the ice barrel will get a slower start rolling. _______________ - Proud padawan of Kueller. - We really are at the beginning of it all. The trick, of course, is to make sure we never find the end. - Bill Bryson, A Short History of Nearly Everything - <gen-e-sis-happy> Liek, you can train, liek, a n00b, but he'll just be a trained n00b... --> Wise words! - "daer SOE me likes your a company i am having your some money for letting me do stuff cos mes the best amd i do it all meself" - Slider |
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Ancient - Ex-Student
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Quote: Umm... what if the barrel with the liquid is missing its top.  The result will be a lot more complex to figure out, since the barrel without water "empty barrel" will excatly satisfy the equation of inertia for a "Hoop", recall my post eariler, the KE<t> will become even lesser than the KE<t> with water in it. But the problem is, the mass of that empty barrel will not equal to the mass of the iced barrel. THerefore, it will involve a lot more physics and calculas calulation to figure that out, which i wont do it here. _______________ -THE ONE WITH THE "STAFF" -BROTHER TO FROSTY -Admitted to University of California, San Diego(UCSD). YAY! |
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Xipkell - Student |
Umm... what if the barrel with the liquid is missing its top. |
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Ancient - Ex-Student
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Quote: Hey what about one of the unique properties of water, think about the frozen tundra where I live. Frozen is the key word. All our 10,000+ lakes, rivers, and streams are nice and solid with ICE for half the year. Now that is funny because well how can ice float? Is that because ice is lighter than water. Hmmmmmm...... ps I live in Minnesnowta! OK, how can ice float on water? IT IS NOT BECAUSE ICE IS LIGHTER IN MASS! BUT INSTEAD, ICE HAS LOWER DENSITY THAN WATER. These kinds of things concerning about density is very basic topic in science. P.S. if you never learn physics before, why bother to argue? _______________ -THE ONE WITH THE "STAFF" -BROTHER TO FROSTY -Admitted to University of California, San Diego(UCSD). YAY! This comment was edited by Ancient on Apr 22 2004 04:29pm. |
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_cmad_ - Ex-Student 
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things float cuz their density is less than the water density. d_water = m_water / V_water = 1 (about 1 anyway) so if something has big volume, at least greater than the mass then it can float _______________ Your friends of today, are your enemies of tomorrow. |
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Ancient - Ex-Student
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Quote: you know ancient, it's sometimes impossible to understand if you are agreeing with someone or not 3th, i am saying that it dosent matter if the water inside the barrel sloshes or not. The ice barrel will still go down there faster _______________ -THE ONE WITH THE "STAFF" -BROTHER TO FROSTY -Admitted to University of California, San Diego(UCSD). YAY! |
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Bubu - Hubbub
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koushka things float not because they are lighter than water. think about a big fat oil tanker. heavy, right? floats, right? i can't wait for the answer to this _______________ make install -not war This comment was edited by Bubu on Apr 22 2004 04:16pm. |
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koushka - Student 
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Hey what about one of the unique properties of water, think about the frozen tundra where I live. Frozen is the key word. All our 10,000+ lakes, rivers, and streams are nice and solid with ICE for half the year. Now that is funny because well how can ice float? Is that because ice is lighter than water. Hmmmmmm...... ps I live in Minnesnowta! _______________ Faithful Padawan of {SKX}Dark Blade My profile pic is luke skywalker
This comment was edited by koushka on Apr 22 2004 02:35pm. |
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3th - Retired 
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you know ancient, it's sometimes impossible to understand if you are agreeing with someone or not _______________ this is the internet, be serious damn it! This comment was edited by 3th on Apr 22 2004 09:38am. |
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Garos - Student 
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I thought they'd hit at the same time tooooo |
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