Plane on a conveyor belt

Maynehead

Sambostar said:

If the women of your dreams was standing at a bus stop with your best mate who saved your life and they both needed a lift but you could only carry one passenger in your car, who would you offer a lift to or what would you do?

Let my best mate drive off in my car and offer to buy the woman a coffee for not being able to give her a lift?

Sambostar

Yeah you've heard it before eh.  Or the ;pair of you get the bus home after coffee....

But what if your mate wasn't insured.  Technically he'd be illegal.  What oif he was really fat and couldn't fit in the seat.  What of aliens landed and confiscated the car?

Maynehead

Sambostar said:

Yeah you've heard it before eh.

I haven't actually, but it is the most optimal solution.

In real life though I'd probably drive past and pretend I didn't see them.

PolarityMan

Alice and Bob want to exchange messages in such a way that they are able to tell if any part of the emssage has been intercepted. Alice a frictionless sphere rotating widershins with an angular momentum equal to the lunar cycle. Bob either always lies are always tells the truth. Ignoring the effect of wind resistance what did I have for lunch today?

mudslide73

Sambostar said:

If the women of your dreams was standing at a bus stop with your best mate who saved your life and they both needed a lift but you could only carry one passenger in your car, who would you offer a lift to or what would you do?

Give em both the car and catch the bus myself..  pick up the props later in the pub. I am married so this is completely hypothetical. 

paul_c2

Sambostar said:

If the women of your dreams was standing at a bus stop with your best mate who saved your life and they both needed a lift but you could only carry one passenger in your car, who would you offer a lift to or what would you do?

I'd cross my fingers and hope that one of the other passengers with me would get off at this stop.

Oh, did I forget to mention I'm a bus driver?

Handsome_Chris

Ha Ha I have solved it.

you put the wheel brakes on. Kick in the thrust. Plane moves forward. The wheels are doing no speed so therefore the conveyor belt has to do nothing. Conveyor belt gets dragged along by friction, or doesn't as the case may be.  Plane takes off.

I can not believe that none of you brainiacs thought of this before.

CabbageCat

Handsome_Chris said:

Ha Ha I have solved it.

you put the wheel brakes on. Kick in the thrust. Plane moves forward. The wheels are doing no speed so therefore the conveyor belt has to do nothing. Conveyor belt gets dragged along by friction, or doesn't as the case may be.  Plane takes off.

I can not believe that none of you brainiacs thought of this before.

I can't believe you would accuse us brainiacs of that without checking whether it was true first.

Handsome_Chris

CabbageCat said:

Handsome_Chris said:

Ha Ha I have solved it.

you put the wheel brakes on. Kick in the thrust. Plane moves forward. The wheels are doing no speed so therefore the conveyor belt has to do nothing. Conveyor belt gets dragged along by friction, or doesn't as the case may be.  Plane takes off.

I can not believe that none of you brainiacs thought of this before.

I can't believe you would accuse us brainiacs of that without checking whether it was true first.

Whether what was true?  

CabbageCat

Handsome_Chris said:

CabbageCat said:

Handsome_Chris said:

Ha Ha I have solved it.

you put the wheel brakes on. Kick in the thrust. Plane moves forward. The wheels are doing no speed so therefore the conveyor belt has to do nothing. Conveyor belt gets dragged along by friction, or doesn't as the case may be.  Plane takes off.

I can not believe that none of you brainiacs thought of this before.

I can't believe you would accuse us brainiacs of that without checking whether it was true first.

Whether what was true?  

Whether no-one had thought of it before. Locking the wheels has been mentioned several times.

Gassage

Frankly, this things taken so long to take off I'm putting in a delay claim on my travel insurance.

Handsome_Chris

CabbageCat said:

Handsome_Chris said:

CabbageCat said:

Handsome_Chris said:

Ha Ha I have solved it.

you put the wheel brakes on. Kick in the thrust. Plane moves forward. The wheels are doing no speed so therefore the conveyor belt has to do nothing. Conveyor belt gets dragged along by friction, or doesn't as the case may be.  Plane takes off.

I can not believe that none of you brainiacs thought of this before.

I can't believe you would accuse us brainiacs of that without checking whether it was true first.

Whether what was true?  

Whether no-one had thought of it before. Locking the wheels has been mentioned several times.

Or has it?

Bidley

http://www.crystalinks.com/matrixspoon_neo.jpg

Chalky

To be fair to the Brainiacs @Handsome_Chris they might have pointed out that your brake-locked tyres would have heated up and burst long before take-off speed was reached, and the speed of a wheel is its displacement in space over time, whether rotating or not, so the conveyor belt would match the speed anyway.

Mkjackary

DiscoStu said:

ICBM said:

The whole point of thought experiments is that you can have solutions which tend to infinity if you need to.

Since I tend to agree with monquixote that those who want to interpret it as a not-real-world-physics question can simply choose whatever conditions they want in order to be right, I will answer this one instead:

DiscoStu said:

The video of the seaplane on the trailer is a completely different scenario to the question posed as the car is pulling the plane forward through the air therefore air is passing over its wings allowing it to take off. 

Not quite. The car isn't pulling the plane forward, or if it is it's unintentional - the plane would fall off the back of the trailer as it got close to flying speed and the friction between the floats and the trailer decreased if it was.

The plane is accelerating through the air under its own engine power. The plane and the car are accelerating at the same rate, or as close to it as the pilot and driver can manage.

The important point being that the plane reaches flying speed not due to the speed of the plane relative to whatever it's resting on, only relative to the air.

And that is really all I'm going to say because it's clearly become a nonsense if you don't just look at the actual physics of it.

The seaplane is being held to the trailer by gravity and friction.
Its engines may well be helping it stay on the trailer but it is the car pulling the trailer which is making air pass over the plane's wings, creating the crucial lift it needs to take off.
Take away the car and the trailer and sit the seaplane on the ground and it won't take off. It might scrape along on its skis but I doubt at a high enough speed to cause lift.
Stick wheels on the bottom though and that's another matter! The wheels don't have drive but they do freewheel along a static ground and allow the plane to move forward properly.

The wheels on the plane in the question are still vital to the puzzle and as they are rotating on a moving surface which has an opposite rotation to the wheels the plane can't move forward.

Here's a 747 at full thrust. Why isn't it moving? Why hasn't it taken off?


Same here, the engines are running but the blocks stop the wheels from turning so it doesn't go anywhere.

If we are to believe the cinematic cockpit shots there are two of the four engines running, although it could be just one, as they only show one of the engines moving from the outside of the aircraft, and if they were running two I would expect then to show us two, or to be able to see the heat coming off of two engines.

But it certainly wasn't all four.

If they could run all 4 at full power while stationary they would have done.

So there is 2 potentially 3 times as much thrust as was shown there a valuable on tap. And they could only do that amount of power for 20 seconds. So imigine 2-3 x that

Sporky

Emp_Fab said:

@Sporky The plane will achieve forward motion because the thrust is against the air, not the conveyor.  The plane will push against the air and move forward.  What the conveyor is doing underneath the wheels is irrelevant

In the real world, yes. In the context of the question, no - you're ignoring that the question effectively locks the wheels in position. Not possible in the real world, but a specified part of the question.

monquixote said:

Maynehead said:

 

This heavily relies on the assumption that each bottle contained an equal amount of pills.

If you don't I'm not sure there is a solution.

I think that is a fair assumption, and even if it isn't, there is still a solution - to wake up.
1) No real doctor would prescribe such a ludicrous treatment, especially if you were about to go on holiday somewhere remote.
2) Pills aren't made to be identical.
3) If you had this condition and treatment, you wouldn't go on a remote holiday.
Thus the most likely explanation is that you're dreaming, which presents a simple solution.

I think the same can be applied to the AOAC problem. To treat it as a real world problem you have to reject part of the specified constraints, at which point you're not answering the question that was asked. To answer the question that was actually asked, you have to accept that the scenario cannot occur under real world conditions.

Garthy

Sporky said:

Emp_Fab said:

@Sporky The plane will achieve forward motion because the thrust is against the air, not the conveyor.  The plane will push against the air and move forward.  What the conveyor is doing underneath the wheels is irrelevant

In the real world, yes. In the context of the question, no - you're ignoring that the question effectively locks the wheels in position. Not possible in the real world, but a specified part of the question.

monquixote said:

Maynehead said:

 

This heavily relies on the assumption that each bottle contained an equal amount of pills.

If you don't I'm not sure there is a solution.

I think that is a fair assumption, and even if it isn't, there is still a solution - to wake up.
1) No real doctor would prescribe such a ludicrous treatment, especially if you were about to go on holiday somewhere remote.
2) Pills aren't made to be identical.
3) If you had this condition and treatment, you wouldn't go on a remote holiday.
Thus the most likely explanation is that you're dreaming, which presents a simple solution.

I think the same can be applied to the AOAC problem. To treat it as a real world problem you have to reject part of the specified constraints, at which point you're not answering the question that was asked. To answer the question that was actually asked, you have to accept that the scenario cannot occur under real world conditions.

This isn't some fancy pants Harvard Professor playing a word game, the original question was posed by a kid on a mailing list in the late 90s who genuinely wanted to know the answer. There is nothing more complicated to it than if you tried to push a rollerskate on a treadmill that you were stood next to.

Emp_Fab

CabbageCat said:

This has been dealt with many times many pages ago. The conveyor is pulling at the wheels. If the plane is moving forwards (without skidding as per monquixote's situation) then the wheels are moving faster than the conveyor which breaches the terms of the scenario. The source of the impetus is what is irrelevant.

Yes - the conveyor is pulling at the wheels.  NOT the plane.  That's the difference.   If you boil it down to Newtonian force equations, the only forces on the plane are the forward thrust from the engines, the drag from the air, gravity pushing the plane down and the ground pushing up, counteracting it.  The last two cancel each other out, so we can ignore them.  That's it.  Nothing else.  Forget about the wheels - they could be spinning at 10,000 rpm, it doesn't matter.  In fact, you can only consider Newtonian forces if you are trying to establish movement.  The engines push against the air, and unless the undercarriage is bolted to the tarmac, the brakes are on or there is any resistance to the rotation of the wheels, those two forces remain the only ones in play.  Forward thrust against the air = plane moves forward.  OK, so the conveyor operator increases the belt speed to match the wheel speed as the plane accelerates - it doesn't matter because the belt is not imparting any force on the plane and therefore plays no part in the equation.  No matter what you do with the conveyor, it's motion, and that of the wheels, are irrelevant because they don't impart any force on the plane.

thumpingrug

I cant believe this has run to 9 pages.   

RocknRollDave

Maynehead said:

Sambostar said:

If the women of your dreams was standing at a bus stop with your best mate who saved your life and they both needed a lift but you could only carry one passenger in your car, who would you offer a lift to or what would you do?

Let my best mate drive off in my car and offer to buy the woman a coffee for not being able to give her a lift?

Shit bus stop if the people waiting at it need a lift, eh...