Cue PH brainiacs - logic puzzle!
Discussion
scorp said:
Anyone care to explain how a wheel, which is on a free spinning bearing is going to be capable of holding back 56,000lb of thrust?
It spins very very fast?
Yeah and............... The wheel isnt what MOVES the jet, its is just there as a convenient interface with the ground. THRUST moves the jet which is independent of the ground
swilly said:
Anyone care to explain how a wheel, which is on a free spinning bearing is going to be capable of holding back 56,000lb of thrust?
It spins very very fast?
Yeah and............... The wheel isnt what MOVES the jet, its is just there as a convenient interface with the ground. THRUST moves the jet which is independent of the ground
Correct, therefore the conveyor can't actually hold the plane back.
So help me, I'm gonna get all technical about the characteristics of bearings in a minute
swilly said:
Anyone care to explain how a wheel, which is on a free spinning bearing is going to be capable of holding back 56,000lb of thrust?
It spins very very fast?
Yeah and............... The wheel isnt what MOVES the jet, its is just there as a convenient interface with the ground. THRUST moves the jet which is independent of the ground
What this thread needs is for the same thing to be explained over and over again in gradually increasing font sizes.
Einion Yrth said:
A site I posted the URL to earlier has a java simulator of the problem which demonstrates the 1/3 - 2/3 proportionality that is the correct answer, ultimately you can believe what you will, but you are wrong.
But if the Java programmer didn't understand the logic, is he going to wriite his simulator correctly?
Meanwhile, being bored, me and a mate decided to create our own analogue simulator, using three Post-Its and the folded up foil from a Kit-Kat. He placed the prize under one Post-It, randomly. I chose a Post-It, randomly (I didn't even look, just randomly picked 1,2 or 3). Now I believe that's an exact replica of the problem (correct me if I'm wrong).
- 100 times, I stuck with my original choice. I 'won' 44 times
- 100 times, I swapped to the other choice. I 'won' 47 times.
Now there's a fairly simple formula is probability theory to determine the probability that Theory A is correct, based on experimental data of a sample size B and result C. I don't have that theory to hand (it's certainly covered in A-Level Pure Maths), and I'll leave it to an A-level student to find that formula, but given the relatively high odds involved in the two theories, and a comparatively high sample size, I would confidently predict that:
- The probability that your theory is correct will be below 10%
- The probability that my theory is correct will be above 80%
Try it yourself. Increase the sample size. Tell us what results you get.
HiRich said:
A site I posted the URL to earlier has a java simulator of the problem which demonstrates the 1/3 - 2/3 proportionality that is the correct answer, ultimately you can believe what you will, but you are wrong.
But if the Java programmer didn't understand the logic, is he going to wriite his simulator correctly?
Meanwhile, being bored, me and a mate decided to create our own analogue simulator, using three Post-Its and the folded up foil from a Kit-Kat. He placed the prize under one Post-It, randomly. I chose a Post-It, randomly (I didn't even look, just randomly picked 1,2 or 3). Now I believe that's an exact replica of the problem (correct me if I'm wrong).
- 100 times, I stuck with my original choice. I 'won' 44 times
- 100 times, I swapped to the other choice. I 'won' 47 times.
Now there's a fairly simple formula is probability theory to determine the probability that Theory A is correct, based on experimental data of a sample size B and result C. I don't have that theory to hand (it's certainly covered in A-Level Pure Maths), and I'll leave it to an A-level student to find that formula, but given the relatively high odds involved in the two theories, and a comparatively high sample size, I would confidently predict that:
- The probability that your theory is correct will be below 10%
- The probability that my theory is correct will be above 80%
Try it yourself. Increase the sample size. Tell us what results you get.
whatever
HiRich said:
me and a mate decided to create our own analogue simulator, using three Post-Its and the folded up foil from a Kit-Kat. He placed the prize under one Post-It, randomly. I chose a Post-It, randomly (I didn't even look, just randomly picked 1,2 or 3). Now I believe that's an exact replica of the problem (correct me if I'm wrong).
You don't mention revealing one of the 'wrong' answers before you are allowed to change your mind, so this is not an exact replica of the problem.
Edited to add: Did you really do this two hundred times? What a waste of time!
>> Edited by GreenV8S on Friday 16th December 14:06
I think it will bounce up and down making the wings snap off, and so the thrust will be lost and the aircraft won't go anywhere.
Then the wings scraping on the conveyor will spark and it'll all set on fire.
Then firemen will try to drive upto the plane, but it's still free-wheeling and so the fire engines can't move forward to put it out.
Then the tyres melt off and the aircraft flies forward before the conveyor can stop and runs into the terminal setting it on fire.
Dave
Then the wings scraping on the conveyor will spark and it'll all set on fire.
Then firemen will try to drive upto the plane, but it's still free-wheeling and so the fire engines can't move forward to put it out.
Then the tyres melt off and the aircraft flies forward before the conveyor can stop and runs into the terminal setting it on fire.
Dave
Mr Whippy said:
I think it will bounce up and down making the wings snap off, and so the thrust will be lost and the aircraft won't go anywhere.
Then the wings scraping on the conveyor will spark and it'll all set on fire.
Then firemen will try to drive upto the plane, but it's still free-wheeling and so the fire engines can't move forward to put it out.
Then the tyres melt off and the aircraft flies forward before the conveyor can stop and runs into the terminal setting it on fire.
Dave
Certainly a lot more sensible than those that say it wont fly.
Tee hee - I read the beginnings of this last Friday, and its still going. Don't post here very often, but felt I had to add to the debate, given I have a 1st class hons from Imperial College in Physics. So here is my take on the problem, including the potential for me to look a complete prick! I couldn't be bothered to read the physics forum...
Anyway - the problem (can't remember the exact wording, but I am certain I know what it is trying to say!) is theoretical in that it is assuming no friction, and I would assume in the original guise of the problem that all feedback provided to the conveyor is instantaneous.
So, we start from the point where there is no movement anywhere - the aeroplane is stationary with regard to both the conveyor and the surrounding air.
The engines then exert thrust, and the aeroplane moves forward in relation to both the surrounding air and the conveyor (conservation of momentum). But - instantaneously the conveyor counteracts - in fact so quickly that the aeroplane does not actually move in relation to the surrounding air. So now the situation is that the aeroplane wheels are moving the aeroplane in relation to the conveyor belt, while it is stationary in relation to the surrounding air.
The engines exert more thrust, and the same thing happens. Instantaneously the speed of the aeroplane in relation to the conveyor increases, while the aeroplane does not move forward in relation to the surrounding air.
And this process continues until the aeroplane reaches maximum thrust (assuming thrust is limited) - i.e. the aeroplane will be moving extremely rapidly in relation to the conveyor belt while it remains stationary in relation to the surrounding air.
So, all the time there is no movement of the aeroplane in relation to the surrounding air, and therefore no lift, and therefore the aeroplane does not take off.
Cheers
Anyway - the problem (can't remember the exact wording, but I am certain I know what it is trying to say!) is theoretical in that it is assuming no friction, and I would assume in the original guise of the problem that all feedback provided to the conveyor is instantaneous.
So, we start from the point where there is no movement anywhere - the aeroplane is stationary with regard to both the conveyor and the surrounding air.
The engines then exert thrust, and the aeroplane moves forward in relation to both the surrounding air and the conveyor (conservation of momentum). But - instantaneously the conveyor counteracts - in fact so quickly that the aeroplane does not actually move in relation to the surrounding air. So now the situation is that the aeroplane wheels are moving the aeroplane in relation to the conveyor belt, while it is stationary in relation to the surrounding air.
The engines exert more thrust, and the same thing happens. Instantaneously the speed of the aeroplane in relation to the conveyor increases, while the aeroplane does not move forward in relation to the surrounding air.
And this process continues until the aeroplane reaches maximum thrust (assuming thrust is limited) - i.e. the aeroplane will be moving extremely rapidly in relation to the conveyor belt while it remains stationary in relation to the surrounding air.
So, all the time there is no movement of the aeroplane in relation to the surrounding air, and therefore no lift, and therefore the aeroplane does not take off.
Cheers
Exige46 said:
But - instantaneously the conveyor counteracts - in fact so quickly that the aeroplane does not actually move in relation to the surrounding air.
Cheers
And that is the nub, how is a conveyor belt going to counteract the force of the engine? All the conveyor will do is act on the tyres, which will just spin the wheels, its force is not transmitted to the rest of the plane.
I should hand that degree back mate
Exige46 said:
felt I had to add to the debate, given I have a 1st class hons from Imperial College in Physics.
...
The engines then exert thrust, and the aeroplane moves forward in relation to both the surrounding air and the conveyor (conservation of momentum). But - instantaneously the conveyor counteracts - in fact so quickly that the aeroplane does not actually move in relation to the surrounding air. So now the situation is that the aeroplane wheels are moving the aeroplane in relation to the conveyor belt, while it is stationary in relation to the surrounding air.
The engines exert more thrust, and the same thing happens. Instantaneously the speed of the aeroplane in relation to the conveyor increases, while the aeroplane does not move forward in relation to the surrounding air.
And this process continues until the aeroplane reaches maximum thrust (assuming thrust is limited) - i.e. the aeroplane will be moving extremely rapidly in relation to the conveyor belt while it remains stationary in relation to the surrounding air.
So, all the time there is no movement of the aeroplane in relation to the surrounding air, and therefore no lift, and therefore the aeroplane does not take off.
Cheers
It is rather alarming to think that somebody who accepts that as a credible explanation was awarded a 1st class hons from Imperial College in Physics.
Honestly, you degree boys should know better. A mere five year City and Guilds craft apprentiship here and I'm about to show you why us shop floor type guys smile at some of the sugestions 
I've already mentioned this a few times, but for the hard of understanding I'll point it out again. The forward motion is supplied by engines which are anchored to the airframe, correct? The counter force is supplied by the wheels which are free to turn. How is any of the opposing force of the conveyor transferred into the aircraft?
Tricky one that, isn't it
Clue, a bearing cannot provide sufficient friction to oppose 56,000 lb of force. The nay sayers need to explain how this magical transferrence of force between the wheels and the airframe takes place.
Plane takes off with rapidly spinning wheels
I've already mentioned this a few times, but for the hard of understanding I'll point it out again. The forward motion is supplied by engines which are anchored to the airframe, correct? The counter force is supplied by the wheels which are free to turn. How is any of the opposing force of the conveyor transferred into the aircraft?
Tricky one that, isn't it Clue, a bearing cannot provide sufficient friction to oppose 56,000 lb of force. The nay sayers need to explain how this magical transferrence of force between the wheels and the airframe takes place.
Plane takes off with rapidly spinning wheels
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