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Topic: The Juggler And The Bridge (Read 2889 times) |
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maryl
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A clown is out hiking in the woods. He comes to a large ravine with a rickety old bridge spanning the width. He needs to cross this bridge. There is a sign posted saying that the bridge`s weight capacity is only 160 pounds. Fortunately, the clown only weighs 158 pounds, clothes and all. Unfortunately, he is carrying a 1 pound apple (his lunch), a 2 pound red nose (an old clown gag) and a 2 pound rubber ball (something to amuse himself as he travels.) Knowing that he cannot risk exceeding the weight limit of the bridge and that he cannot throw away any of his items, how does the clown cross the bridge in only one trip?
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| « Last Edit: Oct 26th, 2003, 3:26am by william wu » |
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Kitty
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Re: Bridge
« Reply #1 on: May 10th, 2003, 2:29pm » |
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You said he weighs 158 pounds clothes and all and if thats not it, he chucked the stuff over (not the same thing as throwing away  ).
By the way how is it a "what happened"?
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| « Last Edit: May 10th, 2003, 2:29pm by Kitty » |
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maryl
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It's a "what happened" because we want to know-what happened. It's classified "situational".
It says he can't throw away any of his items.
And no, there is no play on words.
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Kitty
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Re: Bridge
« Reply #3 on: May 10th, 2003, 2:42pm » |
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He can have someone with him
Or he can throw something from the 'all' away
Or he can eat the apple (that would be a least one pound less) 
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KicksGenius
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Re: Bridge
« Reply #4 on: May 10th, 2003, 4:20pm » |
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One Word: Juggle
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Icarus
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Re: Bridge
« Reply #5 on: May 10th, 2003, 6:28pm » |
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Alas, if the bridge will collapse for any load over 160 lbs, the clown would be hard-pressed to successfully make the trip buck-naked! Go step on your scale - notice that when you first step on, the needle first swings past your weight by 10 to 20 lbs. By stepping slowly and lightly, you can decrease this, but it is extremely hard to limit yourself to a force of 2 Lbs or less above your static weight. Add a 2 lb ball, and he cannot keep the force at or below 160 - as soon as he makes a move, reaction will cause the load on the bridge to increase.
There is little hope of him making it with the apple alone, and no hope at all of getting the other two across. 
(As for eating the apple - it makes no difference whether he carries it inside or outside, he still carries the weight. )
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commando
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Re: Bridge
« Reply #6 on: May 10th, 2003, 8:49pm » |
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Not to mention the trouble of juggling. If holding any single item adds one pound to his weight, throwing any one of them high enough to juggle would probably put the clown over the weight limit (since I believe throwing a 1 pound apple half a meter up makes the clown weight 160 pounds, not to mention throwing and catching items simultaneously or how his moving arms would add greatly to his weight)
Here's a much better approach: without stepping foot on that rickety bridge, put all the stuff on the bridge. All of those things sound like they might roll well. Now the clown shakes his/her end of the bridge enough to create some waves to push the objects to the other edge (but don't shake too violently!). Now, you might say: "but they might roll off the sides!" well, if the clown really is a clown, and clowns can juggle, then certainly a _real_ clown could pull that off  After everything's on the other side, the clown can tiptoe/crawl to the other end, hoping like hell that Icarus isn't right and that at some point s/he'll break the bridge.
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James Fingas
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Re: Bridge
« Reply #7 on: May 13th, 2003, 11:55am » |
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I think you're giving too much credit to the field of civil engineering ... they don't have things accurate down to the pound. Some other reasons why this is a little preposterous:
1) When it rains or the wind blows, the bridge sees loads higher than 160 lbs (unless it's a very short bridge--a couple meters perhaps, in which case he should try jumping, or throwing his objects across first).
2) The loading on the bridge depends on where he is on the bridge. For instance, he could attach pieces of string to his items and drag them across the bridge behind him, spreading out the load. For a reasonably-designed bridge, this should prevent failure.
3) As Icarus says, a 160 lb live load is significantly different than a 160 lb dead load. In my one Civ class, we gave a safety factor of five for live loads (before the other safety factors). So if the sign says 160 lb is the maximum load, they are talking live load (in which case, he's safe). If it really falls down with a force of exactly 160 lb, he'll never make it.
As other people mentioned, juggling or eating the apple don't help. Perhaps he should go back to the circus and borrow 100 helium balloons, wait without eating until he loses some weight, or wait for a cold spell (many materials, especially metals, are stronger when it's cold).
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Lightboxes
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If I were in the clown's situation, I would simply get naked, and take every single item across one by one including my shoes, one by one, and my shirt and pants.
Not wearing the shoes should be enough to allow the clown to walk normal without going over the alloted maximum amount (160 lbs.).
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maryl
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on May 10th, 2003, 4:20pm, KicksGenius wrote:
In the land of Riddleville-this is the answer.
In reality I wouldn't want to try it; although I think if he still is close enough to the edge of the bridge when first placing his full weight on it, and it doesn't snap, then he should be safe-at least if he's quick about crossing.
And if one can juggle riding an unicycle, would it make that much difference crossing a bridge?
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william wu
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Re: The Juggler And The Bridge
« Reply #10 on: Oct 26th, 2003, 4:00am » |
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I guess juggling is the intended answer, but I think this is misleading, because physics explains that such a solution actually doesn't work. I'm surprised someone hasn't explicitly pointed this out already. The riddle should be considered a trick question, in which one should determine why juggling actually does not work.
explanation:
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To sidestep the issue of whether a 160 pound man can cross a 160 pound load limited bridge (since the loads exactly match), let the bridge load limit be 162 pounds. And assume that we don't have the live load problems that Icarus referred to.
By Newton's 3rd Law, the average weight of a juggler over time must equal to the weight of his body plus the weight of the items he juggles. Otherwise the juggler and his items would float away!!! So the average weight of our clown in this case is 158+2+2+1 = 163, which is greater than 162. Thus the clown will surely plunge into the ravine.
Notice that I said average weight over time. That's because the weight of a juggling juggler varies over time -- if you stand on a scale and juggle some small number of objects, the arrow on the scale will fluctuate. Sometimes it will be lower than the sum of the weights before juggling, and sometimes it will be higher. To understand why it can be higher, consider the added downwards force you feel when that 2 pound rubber ball comes down from the sky and falls into your palm.
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| « Last Edit: Oct 26th, 2003, 6:33pm by william wu » |
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maryl
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Re: The Juggler And The Bridge
« Reply #11 on: Oct 26th, 2003, 7:36am » |
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Thanks for coming back on this one William; your are correct in saying it's misleading according to Newton's 3rd law. They should state how juggling would not work.
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Speaker
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Re: The Juggler And The Bridge
« Reply #12 on: Oct 26th, 2003, 5:52pm » |
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Everybody seems to have missed the big issue with this riddle.
Where in the world can you find a 2 pound rubber nose?
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towr
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Re: The Juggler And The Bridge
« Reply #13 on: Oct 26th, 2003, 11:26pm » |
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on Oct 26th, 2003, 5:52pm, Speaker wrote:| Where in the world can you find a 2 pound rubber nose? |
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Since Britain hasn't embraced the Euro, I'd guess there 
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aero_guy
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Re: Bridge
« Reply #14 on: Nov 23rd, 2003, 2:32pm » |
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Ha! that was a good one!
on May 13th, 2003, 11:55am, James Fingas wrote:| In my one Civ class, we gave a safety factor of five for live loads (before the other safety factors). |
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Sometimes I go to Civ lectures just to make fun of their factors of safety.
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