[Guest]

There is a long old bridge across a river(think of it as the only way to cross the bridge). The bridge has grown weak and cannot bear loads beyond a certain limit. On a diversion several kilometers away, there is a checkpoint with a vehicle scale. The men at the checkpoint weighs every vehicle before crossing the bridge and diverts it if overweight. One day, a truck wants to cross the bridge with a lot of load on it. The men at the checkpoint weighs the truck and asks the truck driver to divert. The truck driver quarrels with the men and insists that he can cross the bridge safely without unloading anything from the truck(it is actually the truck that is going to cross the bridge, not the truck driver! ;-)). The checkpoint men allows him to cross and warn him that even if a sparrow sits on the truck over the bridge, the bridge will fall. The truck driver agrees and goes on his way. When he was crossing the bridge, a few birds gathers around the truck and finally sits on the truck. The checkpoint men were watching all this, and when they saw the birds sitting on the truck, they closed their eyes because of the fear of the falling truck!! But when they opened their eyes, they were astonished to see the truck passing the bridge safely!!! How did the driver managed to do that??

[Guest]

...the amount of fuel to drive from the checkpoint to the bridge was enough loss of mass that the added weight of the birds amounted to equal or less than the bridge limit?

[Guest]

The birds that sit on the truck are not sparrows, they are smaller(like hummingbirds).

[pdqkemp]

The only point at which the bridge could break with the additional weight of a bird is the very middle of the bridge where it is most vulnerable. The birds landed on the truck about 3/4 of the way through the trip, so there was no danger.

That coupled with the amount of fuel lost by the time the truck is more than 1/2 way. (Taken from the first answerer.)

[Guest]

The truck was delivering bird food and the birds ate it thus lessening the weight?

[Guest]

The truck was delivering bird food and the birds ate it thus lessening the weight?

HAHAHA!!! I love that answer!!!

[Guest]

I believe the weight of the fuel expended to reach the center of the bridge made up for the tiny amount of weight added by the bird.

[Guest]

fuel had lessened that much that the weight of sparrow would be equal to weight of the fuel lost during travel. thus the truck could get through easily.

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Edited July 24, 2010 by parik

[MissKitten]

i agree with the first poster as well.

[Guest]

Everyone at the checkpoint had birds on their mind

Because the truck was delivering birds. They settled down during weighing, so the truck weighed heavy, but the driver pointed out that the jostling ride means that many of them are in flight during the crossing (and a partially open trailer would allow the force of lift to not increase the weight of the truck).

[Guest]

Anza: But then the weight of the bird food would still be in the birds. Here's my answer:

The truck driver had to go to the bathroom beforehand, and so lessend his weight.

Edited July 26, 2010 by NickFleming

[MissKitten]

lol ^