# Bridge over troubled waters

1. Nov 22, 2004

### iknownothing

My first post... So be nice, or I'll blast you with a phaser...

You are at one side of a canyon at the start of a bridge. The only way to cross the canyon is over the bridge. (no tricks to this, just a normal crossing of the bridge, don't try to walk on water here) On you side are 3 gold bars, each weighing 3kg. You weigh 78kg. The bridge can only support 80kg without breaking. How do you get yourself accross with your new found wealth, without falling through the bridge?? --And no, you can't throw it accross.

Last edited: Nov 22, 2004
2. Nov 22, 2004

### shibumi

as far as the question goes i know that it has to do with applied force and kinetic energy but the math is beyond me.

Last edited: Nov 22, 2004
3. Nov 22, 2004

### Galileo

You wait untill you weigh an ounce.

...or at least 7 kg lighter. Then go across with the gold bars.

4. Nov 22, 2004

### shibumi

true enough but i think that there is an impetus of time involved? where the person needs to be across within a certain time frame that doesn't allow one to wait until they are emaciated. good try! :)

5. Nov 22, 2004

### marcus

break up the gold bars into smaller chunks and make several trips
each time taking a chunk weighing less than 2 kg

6. Nov 22, 2004

### matthyaouw

Go round?
either that, or put the gold bars in your bag, cut the ropes of the bridge, and swing across indiana jones style, before undertaking a daring climb up the other side.

(in other words, I havn't the foggiest idea!)

7. Nov 22, 2004

### tribdog

I think Ive got it.tie a rope to the bricks, walk across the bridge then pull the bricks across..

Last edited: Nov 22, 2004
8. Nov 23, 2004

### albengineer

9. Nov 24, 2004

### tribdog

I gave it in white letters in the post above yours. you have to select it to see it.

10. Nov 24, 2004

### Moonbear

Staff Emeritus
Nah, I think this is the answer (in white text):
You have to perfectly synchronize your jumping (or hopping) across the bridge with your juggling of the gold brick so that you aren't touching the brick when you're touching the bridge. You better practice it a bit before trying it for real, it would require immense coordination.

11. Nov 24, 2004

### bjr_jyd15

I'm sure if you can induce enough vomit you can lost a kg. Then make trips with one gold bar at a time. But be sure to brush your teeth afterwards.

12. Nov 24, 2004

### Dual Op Amp

Maybe....
Take off all your clothes, then walk with one bar at a time.

Last edited: Nov 24, 2004
13. Nov 25, 2004

### DaveC426913

Not sure if you were serious tribdog, but this won't work:

"...You have to perfectly synchronize your jumping (or hopping) across the bridge..."

If you could actually decrease your weight by continually jumping, a lot of people would be doing it instead of dieting. Your weight will far exceed 80kg every time you land.

Personally, breaking the bricks in half is the most plausible solution. This problem doesn't indicate if you can use props, like tools to chop, melt or otherwise dissassemble anything. Just seems a little simplistic for a puzzle.

Then again, if you can use props, the rope trick would work just fine.

14. Nov 25, 2004

### tribdog

I wasn't the one who came up with that solution. That was moonbear.

15. Nov 26, 2004

### Moonbear

Staff Emeritus
But in the puzzle, my weight alone is only 78 kg, not 80 kg. Do you think the puzzle would take into account real physics? I wasn't reading that deeply into it.

Though, actually, continually jumping is an excellent way of losing weight. If more people jumped continuously, they wouldn't need to diet! :rofl:

But, aha! Working together can help sometimes...maybe the solution is to jump around for a while, run back and forth the bridge a few times, pee, whatever, until you've lost a kg, then you can just walk across carrying the gold with no problem.

Then again, no gold is worth walking across a bridge with a weight limit within only 2 kg of my weight! I want to see those error bars first!

16. Nov 26, 2004

### marcus

when I suggested this back a ways in post #5 of this thread, i didnt think anybody would be wondering how you'd break a gold bar in half-----if you found one in a canyon

canyons have rocks. I'd put the bar between two rocks and chop it in the middle with a third rock.

how big is a 3 kilo gold bar?

gold is 19 times denser than water so the volume of a 3kg bar is about 1/6 of a liter.

that is less volume than an ordinary kitchen measuring cup

and gold is soft, so I think that volume of gold formed into a bar
would be something you could hack or bust in half without too much trouble

warn moonbear not to jump on a fragile bridge

17. Nov 26, 2004

### Moonbear

Staff Emeritus
Well, if you can hack it or bust it in half in the middle of the woods, surely you can also stretch it into a very fine wire, long enough to make about twice the length of the bridge. Grab one end, leave the other end behind and you have no more than half the weight of the brick with you on the bridge when you are at the other side. Then just pull the rest across. On the downside, be very careful not to get a tangle in the wire, or you'll drag the whole clump onto the bridge and fall to a horrible death.

Aye aye cap'n! :tongue2:

Out of curiosity, how did I get to the side of the bridge I'm on anyway? I have to cross the bridge to get to the other side of the canyon, but is that the right direction to get home? Maybe all I need to do is grab my three bricks of gold, toss them in my backpack, and turn around and walk back out the way I came from.

18. Nov 26, 2004

### tribdog

One time I was out camping and when dinner time came I grabbed a can of chili then realized I didn't have a can opener. I beat the hell out of that can trying to open it. That can got the best of me and I had to settle for chips for dinner. My point is: you can't break a bar of gold with a rock. Go grab a rock and break a silver dollar in half and I'll believe you could break the gold.

19. Nov 26, 2004

### iknownothing

Sorry Guys and Gals,

I really dont have an answer to this one. :yuck: I put it here hoping to find a physics answer. But I like the one saying dont cross the bridge, just walk the other way.

....Then again, could you create a rope to drag the bricks by pulling pieces of the bridge off? ...I've never made rope, but I'm sure I could if there were 3 gold bricks wanting me to! :rofl:

20. Nov 26, 2004

### Moonbear

Staff Emeritus
First you need to find the right type of rock, then find another rock, and chisel the rock into a spear point, try not to smash your fingers with either rock or cut your hand open on the sharp edges, then, no problem, you have a can opener. I used to carry around one of those 10 cent can openers you can buy in army surplus stores that goes on your keychain. Stopped carrying it when they banned anything with a point on it from airlines since I fly a lot and would forget to take it off the keychain. You'd be amazed how often you find yourself in the middle of the woods in need of a can opener. :tongue: You could have tossed the can on the campfire and when it exploded, then retrieve the chili...just don't stand too close when you do that. I hear chili can shrapnel really burns! :rofl: