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Topic: a cargo of pigeons (Read 506 times) |
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Benny
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a cargo of pigeons
« on: Jun 18th, 2009, 12:19am » |
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The driver and his commercial transport vehicle weigh 10 tons. His cargo of 200 uncaged sleeping pigeons weighs 200 lb. The driver approaches a 10-ton-limit bridge, stops, gets out, bangs on the side of the vehicle to make the pigeons fly about, gets back in and drives over the bridge safely. In practice his actions were correct because he managed to cross the bridge safely, but was his reasoning correct in theory?
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Grimbal
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Re: a cargo of pigeons
« Reply #1 on: Jun 18th, 2009, 1:41am » |
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"Uncaged", does it mean they are sitting on top of the truck?
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towr
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Re: a cargo of pigeons
« Reply #2 on: Jun 18th, 2009, 1:42am » |
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on Jun 18th, 2009, 12:19am, BenVitale wrote:| was his reasoning correct in theory? |
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No, and mythbusters proved it.
http://kwc.org/mythbusters/2007/04/episode_77_birds_in_a_truck_bi.html
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| « Last Edit: Jun 18th, 2009, 1:42am by towr » |
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Benny
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Re: a cargo of pigeons
« Reply #3 on: Jun 18th, 2009, 11:02am » |
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on Jun 18th, 2009, 1:42am, towr wrote:
Thanks for the link.
Could you apply the same reasoning to the following problem :
Imagine John, a party magician, is carrying three pieces of gold each weighing one kilogram. While taking a walk he comes to a bridge which has a sign posted saying the bridge could hold only a maximum of 80 kilograms. John weighs 78 kilograms and the gold weighs three kilograms.
John reads the sign and still safely crossed the bridge with all the gold. How did he manage this?
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If we want to understand our world — or how to change it — we must first understand the rational choices that shape it.
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towr
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Re: a cargo of pigeons
« Reply #4 on: Jun 18th, 2009, 11:18am » |
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on Jun 18th, 2009, 11:02am, BenVitale wrote:Not by juggling, in any case. You weigh more then your weight+gold bars when you throw them up. (But of course, you also weigh more whenever you make a step and push your body up).
I'm not sure magicians are well known for their juggling skills anyway, usually it's a clown in this riddle, I think.
Maybe he used magic 
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Grimbal
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Re: a cargo of pigeons
« Reply #5 on: Jun 19th, 2009, 12:40am » |
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More realistically, the weight limit of a bridge always provides a comfortable safety margin. If the bridge says 80 kg it is probably designed and tested to hold 160. 1 kg over the limit is safe.
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MathsForFun
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Re: a cargo of pigeons
« Reply #6 on: Jun 22nd, 2009, 7:38am » |
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on Jun 18th, 2009, 12:19am, BenVitale wrote:| The driver and his commercial transport vehicle weigh 10 tons. His cargo of 200 uncaged sleeping pigeons weighs 200 lb. The driver approaches a 10-ton-limit bridge, stops, gets out, bangs on the side of the vehicle to make the pigeons fly about, gets back in and drives over the bridge safely. In practice his actions were correct because he managed to cross the bridge safely, but was his reasoning correct in theory? |
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It depends on whether the lorry container is airtight: if it is, then all the forces inside it must balance - so the weight of the pigeons must continue to push down the lorry. If the lorry container resembles a cage, then the force needed to keep the birds in the air can be dispersed away from the lorry.
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Grimbal
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Re: a cargo of pigeons
« Reply #7 on: Jun 22nd, 2009, 7:49am » |
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If the back of the truck is a cage, the driver could teach the pigeons to each stick one wing out from the side. With the speed of the truck that would provide some lift.
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Whiskey Tango Foxtrot
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Re: a cargo of pigeons
« Reply #8 on: Jun 23rd, 2009, 7:05pm » |
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Slightly unrelated, but had to post this after the "Mythbusters proved it" line.
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"I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use." - Galileo Galilei
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