Maximizing Bridge Capacity: A Weight Distribution Dilemma

[ascky]

Well it depends how you define supporting '80kg without breaking'...

If you're standing close to one side of the bridge, you'll be exerting more force on the side you're closer to. But if you stood in the middle of the bridge, the force would be shared equally between the two endpoints of the bridge...

Assuming you can jump to the middle holding your gold bar...?

Don't know if the math works out

 

[ascky]

Actually if the elevation up to the bridge was right, couldn't you get the middle of the bridge close to the turning point of the parabolic jump? Would that help...? Confusing.

 

[ascky]

Actually I think that's all drivel. If you lie on the bridge to give a greater surface area with your gold bar on top of you?

 

[Dual Op Amp]

Just jump, surely you can swim. Then, climb up the mountain to the other side.

Take off all your clothes, rip them into long threads. Tie them around one gold bar at a time, then pull them across the bridge once you're safely on the other side.

 

[Up_Creek]

Actually, if I came upon said gold bricks, and we're assuming that all this info is readily available (IE: a sign that tells me how much the bridge can handle ect) and there was a way of knowing exactly what my weight is, i'd be suspicous.
1.) Why would someone leave gold bricks infront of the bridge?
2.) Why are the bridge's tolerances only 1 kg over my weight?
3.) GOld bricks, seemingly in the middle of nowhere, and I'm the only one around

I've got to believe someone's watching me. It's just too like a trap or something. Why am I wandering the barren canyon-lands anyway? Surely not on a quest for gold. Enlightenment perhaps? A classic example of foregoing the rewards to continue on my way. I bet Buddah would know the answer to this... ;)

And since this bridge is a bridge over 'troubled' water, I'm assuming I can't swim for it (alas, I can't even swim). Perhaps the bridge is metaphorical. Like the song. The gold represents the trappings of narcotics. The point is to not take the gold across and you'll be better off, hence leaving the drug problem, the troubled waters, and if you're lucky, Simon and Garfunkel, behind me.

Do I win?

Jordan Veale

 

[Dual Op Amp]

Cut off your arm, then carry the gold bars. Go back, pick up your arm. Then, with your new found wealth, have your arm sewn back on.
Then, buy a BIG house and a Jaguar XJR!


Real Answer:
The rope is what is taking all of the tension, it's taking the weight. Take off every other step, so that the weight is cut in half. Then, grab the bars, and carefully walk across the bridge.

 

[BobG]

Actually a similar problem had one tie rope to the load, lower the bars to the bottom of chasm (assuming rope long enough to reach down to bottom of chasm, but not long enough to reach across the bridge), cross bridge (hopefully with less than 2 kgs of rope) and pull load up other side.

I think you're talking about getting 3 balls across a river on a boat. There's a possible solution depending on the density of the balls. The density would have to be less than 3 to reduce the force on the boat enough to get them across.

For this problem, we're given the fact that they're gold bars. The density of gold is around 19 (pure) to 16 (fairly impure). Tribdog's is the simplest solution.

A really big helium balloon would also solve the problem. The advantage of this solution is you could inhale the helium and talk to yourself in funny voices after crossing the bridge.

 

[Moonbear]

What the question doesn't tell you is there were originally 4 bars of gold, but the original owner didn't know much about physics, and he and his gold bar are down in the river somewhere.

Wait, Dual Op Amp's answer leaves me wondering just what part of the bridge can't support weight above 80 kg. Is it that the supports are weak, or the boards? Where's the weakest point that's going to fail if I step on with too much weight? Maybe it's just one anchor point, on the side I'm on, where the rope is starting to fray. So, I take my gold bars, grab one of the ropes, hang on tight, and when the anchor fails, I swing to the other side, then climb up the planks like a ladder. Um, assuming this is a rope bridge we're talking about. (I'm getting an image of Wile E Coyote slamming into the side of a cliff at the moment...ouch!). Though, that's how Indiana Jones would do it.

But if it's just weak planks across the bridge, you could walk along the railings, or climb under or up (depending on the structure) and hang from the supports (this approach probably works best if you're a trapeze artist).

Oh, oh, oh, I just thought of another answer. If the bridge is there, then it must have been possible to get to the other side before the bridge was built, otherwise it couldn't have been built. So, just find the long way around the bridge builders used. Erm...you might have to recruit some beavers to build a dam to make the river passable.

 

[Gokul43201]

psst BobG, there was no mention of a river anywhere in the question. I think Astronuc was lowing the bars down to the conyon floor (or riverbed, if need be).

 

[ceptimus]

These 'maximum bridge load' warning signs always have a safety factor built in, and you can be sure it's at least 10%.

So I'd just pick up the gold and tip toe over. If I was confident in my 10% safety margin, I could even take all three bars at once, and I might do that, depending on how long the bridge is, and whether or not there are any shady characters about who might steal *my* gold.

 

[Dual Op Amp]

Well, it said bridge over troubled waters, so it's assumed there is a river. But, it's the rope that takes all of the weight.The object that is anchored to each side of the canyon is the one that takes the tension. So, the only thing that the steps are doing is just adding weight.

 

[BobG]

Yeah, I had to go back to make sure I read it right.

Canyon? Bridge over troubled waters? What body of water would you expect to find at the bottom of a canyon?

At least you'd better hope so. Otherwise you'll be in for a pretty big surprise when you jump off the cliff into the canyon.

 

[Gokul43201]

Guess I forgot about the troublesome waters. You can have a canyon where the river's run dry, can't you ?

<holding blow-torch to the Colorado>

 

[FutureVeterinarian]

This is my first post, so, go with me here. Walk across the bridge, and pray while you're walking! If you remove you're shoes, and anyother item causing weight, maybe you can make it. Or, you can call a helicopter using a phone, and pay the helicopter man with you're new found wealth!
Nah... here's what I think the real anwser is. It's in white, so, highlight it.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If there is a bridge, there is obviously civilization on both sides of the bridge, otherwise, what's the bridge there for? So, if there is civilization of both sides of the bridge, go back to a city on your side of the bridge, and ask someone lighter than you to carry the gold across the bridge in exchange for one of the gold bars. It's worth it, right?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
So, what do you think? Do you think it could work? :shy:

 

[bjr_jyd15]

Future Vet, I'm almost sure that the civilization would eat you alive. They'd take every one of your gold bars and teach you and everyone else in florida how to vote. ;)

 

[Bartholomew]

It says you can't THROW the gold bars across, but it never says you can't KICK them. Or make a primitive sling out of your shoelaces. Or you could use a rock to hammer the bars into frisbees... no wait, that counts as "throwing."

 

[Dual Op Amp]

Future Vet, I'm almost sure that the civilization would eat you alive. They'd take every one of your gold bars and teach you and everyone else in florida how to vote. ;)

I agree, and if that doesn't work out, you could always recount.

 

[DaveC426913]

So, can we have a hint?

 

[DaveC426913]

"...without falling through the bridge..."

Just noticed this in the original question.

The whole bridge won't collapse into the canyon, just the part you're standing on. That allows for many of the solutions mentioned already.

 

[tribdog]

Actually, it's hard to find gold bars even 1 kg. Most that are commonly available are far smaller than that. Which means you're hallucinating the whole thing, the bridge doesn't really exist, and if you try to cross it, you're going to fall into the gaping chasm.

I missed this one the first time through. I used to work at a gold mine (Battle Mountain Gold Company) and got to hold one of the big bars

 

[DaveC426913]

Hey, were we ever going to see an answer to this one?

 

[Gale]

Hey, were we ever going to see an answer to this one?

Sorry Guys and Gals,


I really don't have an answer to this one. I put it here hoping to find a physics answer.

there is no answer...

 

[minger]

I think I actually have an answer. My first reaction to this problem was to throw it up and do the jumping thing. If you "cushioned" your landing enough, I think it would be possible, however here my real answer.

The bridge somehow will fail to weight, and I think we agree that the ropes on this bridge resist the entire load. Sooooo...take a few of the planks off and step over the hole in the bridge. What I would do is take off like every other plank until I was half way over the bridge, then go back and take all 3 bars. (surely I've thrown 9kg of wood off of the bridge).

;)

 

[xJuggleboy]

Ok here is my go at it...

If the bridge has planks running across it to make the walkway. And one plank can only hold 80Kg.

With your right foot on the ground. Put your left foot on the 3rd plank. Move all the bricks one at a time to the 2nd plank. Move your first foot to the 1st plank then your other foot to the 4th. Move the bricks to the 3rd plank. And so forth till you get all the way across.

Not much of a solution but It should work

One other tought... If you steped on the crack between 2 planks they would both be supporting your weight and shuldent break... Maybe...

 

[Automagman]

Ok here is my go at it...

If the bridge has planks running across it to make the walkway. And one plank can only hold 80Kg.

With your right foot on the ground. Put your left foot on the 3rd plank. Move all the bricks one at a time to the 2nd plank. Move your first foot to the 1st plank then your other foot to the 4th. Move the bricks to the 3rd plank. And so forth till you get all the way across.

Not much of a solution but It should work

One other tought... If you steped on the crack between 2 planks they would both be supporting your weight and shuldent break... Maybe...

I think we are assuming that the planks are sturdy and the rope is not, it would be too easy the other way around.

I am going to try this with as many restrictions as i can think of, this is first post so be gentle

...I was actually going to try to figure this out but then i remebered i had homework to do.

here is my BS answer.
Since the entire universe is holographic i will use my jedi powers to close the canyon and walk across the newly formed land bridge.

 

[Jimmy Snyder]

1. How wide is the canyon?
2. How high is the bridge?
3. How deep is the water?

 

[DaveC426913]

"...take a few of the planks off and step over the hole in the bridge. What I would do is take off like every other plank until I was half way over the bridge, then go back and take all 3 bars. (surely I've thrown 9kg of wood off of the bridge).
"

This is the best answer I've heard yet, although the original problem doesn't mention the construction of the bridge.

 

[minger]

"...take a few of the planks off and step over the hole in the bridge. What I would do is take off like every other plank until I was half way over the bridge, then go back and take all 3 bars. (surely I've thrown 9kg of wood off of the bridge).
"

This is the best answer I've heard yet, although the original problem doesn't mention the construction of the bridge.

Thank you I imagine if this bridge can only hold that much weight, it must be pretty shotty built

 

[nipwoni]

Exchange the gold bars for paper money (much lighter) then walk across. If you still want gold you can buy some at the other side. :)

 

[mapper]

Id use one gold bar to pay the locals to build me a better bridge. :)