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More ways to get Braingle...

A Truck and a Bridge

Science brain teasers require understanding of the physical or biological world and the laws that govern it.

 

Puzzle ID:#374
Fun:*** (2.43)
Difficulty:** (1.64)
Category:Science
Submitted By:JoeyChavez**

 

 

 



A truck comes to a 1000 ft. long bridge and stops right before going on to it to read a sign. The sign says that the maximum weight the bridge can hold is 4 tons, which is the exact weight of the truck. So the truck starts going on the bridge. About halfway over the bridge a little bird lands on the top of the truck. Does the bridge break?


Answer

No, because by the time the truck is halfway across the bridge it has burned enough gas which brings its weight down to let the bird sit on it without the bridge breaking.
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Comments

blazeoner
Jun 09, 2001

What about the weight of the truck driver?
KmartSmile
Jul 16, 2001

what about the drivers weight?
Pongalopete
Sep 07, 2001

Ditto what about the driver's weight was it included?
randyeatmon
Oct 06, 2001

"Gas" and fuel are commonly interchangeable. If the fuel were Diesel and the engine in good condition then it would be an arguable proposition. The "Bird" could also have been a well fed Eagle. Too vague.
(user deleted)
Nov 15, 2001

that is one innefficient truck to use a birds weight if fuel in 500ft
(user deleted)
Feb 22, 2002

I am sure when engineers are designing bridges they take into consideration exrta weight. And anyway birds don't weigh that much...
bluetwo*
May 29, 2002

elsie is absolutely correct. the engineers build in a certain margin of safety in the design. just because a bridge is rated to 4000 lbs does not mean that it will crumble to the ground when 4100 lbs of force is applied. it is, however, a "safe" figure. by the same token, rooms can hold more than their stated max capacity, but it is due to safety concerns in the event of an emergency that those capacities are stated.
jonnyonline
Jan 24, 2003

what if the bird landed on the truck, latched it's claws around a part of the roof and started flapping upwards, then its weight would be negligible.
Mogmatt16Ava*
Jun 29, 2004

no, becuase then the bird would be pushing air down equal to it's weight.
TehIgnored*us*
Mar 03, 2006

When in danger or in doubt, run in circles scream and shout....



and no...im sorry but this is a VERY weak riddle....
Crazycriely*
Mar 25, 2006

well i said no, but i dont think the gas or the bird would be very significant weight so i dont think it would break.
Vigo95Aus*
Mar 25, 2006

i agree crazycriely !
AtropusAnz*
Apr 05, 2006

I'm with elsie on that one...

It's like those elevators that have a limit of 9 people.. there is a margin of error built into any structure that people want to keep up. Redundancy is one of the fundamental principles in architecture.
calmsaviorAus*
May 10, 2006

whys everyone talking about the weight of the driver?
Mellew*us*
Jul 30, 2006

but what if another car is on the bridge also??
cyberstar5150*us*
Aug 04, 2006

Yeah... if you're using a bird's weight in gas to go that far, you're in trouble.

The true reason it would be okay is because engineers have a factor of safety built in... and would NEVER put a sign up that says the absolute maximum or people like this guy would try to max out and destroy the bridge.
cyberstar5150*us*
Aug 04, 2006

For those of you who aren't engineers and don't know what factor of safety is:

Factor of safety takes into account the worst case scenario for that bridge (say the worst case is 1000 lbs) and makes it stronger to avoid having it break (say they make it able to tolerate 1500). The factor of safety for such a bridge is 1.5.
rrn0rrnrrnY*us*
Sep 08, 2006

simple teaser, simple answer:No
LeafFan4life*
Mar 02, 2007

i got answer no but for wrong reason here is my reasoning:
Most signs such as elevators but the maximum weight it can with stand on it but they usually put less than it actually is just incase so if it said can hold 1200pounds it can probably hold more than that but just for safety they put less.
deadsnakebitingAus
Mar 14, 2007

Before looking at the Answer or the other Comments, "I swear no peeking - I'm out here on a limb, gang;" no, the bridge will not break. Ratings are set at a weight that does not come close to the actual limit (maybe 15-20% less) for exactly these types of situations. Now, I will go look at the answer and see how I did!
deadsnakebitingAus
Mar 14, 2007

PS. Just a follow up... the given answer shows a little thought - but the rating / actual maximum weight still stands - look it up! Otherwise lots of bridges would fail because most truckers use the SWAG method to determine their weight. SWAG = Scientific Wild-Ass Guess!



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