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        riddles >> what happened >> Big Truck-Small Bird
        
(Message started by: maryl on Jun 5^th, 2003, 2:51pm)

Title: Big Truck-Small Bird
Post by maryl on Jun 5^th, 2003, 2:51pm

A large truck is crossing a bridge 1 mile long. The bridge can only hold 14000 lbs, which is the exact weight of the truck. The truck makes it half way across the bridge and stops. A bird lands on the truck. Does the bridge collapse? Give a reason.

Title: Re: Big Truck-Small Bird
Post by Icarus on Jun 5^th, 2003, 6:54pm

The bridge collapses because: [hide] The truck was electric.[/hide]

Title: Re: Big Truck-Small Bird
Post by maryl on Jun 6^th, 2003, 11:45am

on 06/05/03 at 18:54:49, Icarus wrote:

The bridge collapses because: [hide] The truck was electric.[/hide]

Icarus, if you would have said the opposite you'd be right.

Title: Re: Big Truck-Small Bird
Post by Icarus on Jun 6^th, 2003, 8:26pm

Now - I had to look hard to find a scenario where the bridge collapses! (Other than the ordinary "bring some reality into the equation" approach which points out that only a fool would attempt to cross a bridge stressed to it's very limit, since dynamic loads will surely push it over that limit.)

The least you could do is be a little appreciative! :D

Title: Re: Big Truck-Small Bird
Post by mistysakura on Jun 7^th, 2003, 9:22pm

Well, no one said tht it wasn't electric. ;)

Title: Re: Big Truck-Small Bird
Post by maryl on Jun 8^th, 2003, 10:27am

on 06/07/03 at 21:22:57, mistysakura wrote:

Well, no one said tht it wasn't electric. ;)

True, very true; it should be reworded to say how can this humongous truck get across with a bird landing on it halfway there? Oh well.

Title: Re: Big Truck-Small Bird
Post by Redingensian on Oct 28^th, 2003, 3:16pm

Doesnt a truck weigh more when moving?

Title: Re: Big Truck-Small Bird
Post by Icarus on Oct 28^th, 2003, 5:23pm

Well, there is the relativistic mass increase... But at the speeds of even the fastest land vehicles this amounts to picograms or less. I.e. considerably less that than the weight effect of the driver breathing. Other than this infinitesimal weight increase, motion has no effect on weight.

However, there are also the dynamic loads. The truck rises and falls on its axles as its speed changes, and it presses horizontally on the road surface, some of which is converted in to vertical load by the bridge structure. (These loads are additional forces on the bridge - but they are not weight.)

Since we have discussed thoroughly the reality of this situation in other threads (there is one about a clown crossing a bridge whose standard answer is simply wrong for exactly this reason), I choose to ignore the issue here, and instead find another way in which the "correct" answer could be wrong!

Title: Re: Big Truck-Small Bird
Post by towr on Oct 28^th, 2003, 11:32pm

One might also consider it takes time for something to buckle under pressure, so if an object is moving the surface it is on is less likely to collapse the the faster the object moves (but it must move smoothly, since bumps get amplified by speed).

Title: Re: Big Truck-Small Bird
Post by Jack Z. on Nov 1^st, 2003, 4:54am

Q: A large truck is crossing a bridge 1 mile long. The bridge can only hold 14000 lbs, which is the exact weight of the truck. The truck makes it half way across the bridge and stops. A bird lands on the truck. Does the bridge collapse? Give a reason.

this is an very ez question
A: By the time it got to half way (1/2 mile) it would have used enough fuel to lighten down. With the fuel lose the bridge could easierly support the truck and the bird.

solved by J.Z ;D
;D

Title: Re: Big Truck-Small Bird
Post by towr on Nov 1^st, 2003, 10:05am

Ah, now I understand Icarus' reply..

Title: Re: Big Truck-Small Bird
Post by Icarus on Nov 1^st, 2003, 7:00pm

Let's see - that's you and mistysakura, and maryl after a little nudging... A small list! ::)

Title: Re: Big Truck-Small Bird
Post by aero_guy on Nov 23^rd, 2003, 2:24pm

Does J.Z. think he is the first to solve these when he posts like that? He doesn't seem to realize that they were solved after the first reply.

Title: Re: Big Truck-Small Bird
Post by Icarus on Nov 23^rd, 2003, 6:45pm

I suspect Jack is rather younger than you, and considerably more so than I. He also may have not been aware of hidden text at the time. And he probably did not pick up on what my answer was about either, and simply noted that the "correct" answer had not been given.

Title: Re: Big Truck-Small Bird
Post by Jess_13 on Feb 21^st, 2004, 8:51am

NOPE the bridge didnt collaps...one little bird cant make a whole bride fall down...14000 lbs is the approximite weight it can hold//

Title: Re: Big Truck-Small Bird
Post by pedronunezmd on Jun 15^th, 2004, 6:34pm

Reading this thread months after it had been solved, I must say that Icarus's initial response was probably the best way I've ever seen an "answer" posted for any riddle. Belated bravo!