Riddle Me This.....Before My Brain Implodes!

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Raffi_B

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Here's a riddle...

Find the next number in the series.

1, 11, 21, 1211, 111221, 312211, 13112221

A few hints:

The numbers are in base-10. The number does not need a calculator/computer to calculate (not even basic functions such as + or -). It can be done completely mentally... not even pencil/paper is necessary.
 

ant75

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Hmmm, i've never been good at physics, but i don't think the fact that the wheels of the plane have no power is relevant. So far nobody has mentioned anything about friction and the fact that the plane's mass rests entirely on its wheels (until it has taken off). In this regard wheels do a bit more than "just spin".
But anyway most controversy here seems to come from the interpretation of the original text, not from physics principles.

edit : now somebody has mentionned the weight of the plane ;)
 
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shadow_dragon

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ant75 said:
Hmmm, i've never been good at physics, but i don't think the fact that the wheels of the plane have no power is relevant. So far nobody has mentioned anything about friction and the fact that the plane's mass rests entirely on its wheels (until it has taken off). In this regard wheels do a bit more than "just spin".
But anyway most controversy here seems to come from the interpretation of the original text, not from physics principles.

If you put a car on a conveyor teh wheels would be relevant because the forward motion of the car comse from the wheels so the car would stay stationary on the conveyor.

However with a plane the forward motion is provided by the engine, so the plane will simply drive off the conveyor no matter how fast the converyor goes.

If teh question stated. "If i a plane was tied down onto a conveyor belt that ran exactly the same speed as it's wheels in the opposite direction. Would it take off?" Tehn the answer would be no, but currently it is yes.

I'm not sure if that makes sense but it's the simplest way i could think of to describe it.
 

Zarkazm

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Jan 29, 2002
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This reminds me of a debate about whether or not wearing lead plates could make a man fall faster.
 

BobCobb

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A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?

Ok, since the conveyor belt speed is equal to the plane speed, we can assume that with no outside forces involved the system is in equilibirum in reference to the earth. In other words, the velocity is equal to zero.

Lift = liftcoefficient * density * (Velocity^2)/2 * wing area

Since the velocity is equal to zero, there is no lift.

Therefore, no the plane will not take off. Planes do not take off without lift.

This is simple physics folks. If theres ever a concept you don't understand, there are equations that took humanity thousands of years to figure out. Use them.
 
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Airmoran

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The "lead pants" thing is a straight-up understanding of physics. This plane thing is a riddle intended to fool people into thinking it's a simple matter of aerodynamics. asdlfkjas;ldkfjasldjfasdf.

Anyways, alright. It's true, the plane would need to be moving to lift off. You'd think that with the conveyor belt, the plane would stay still, buuuuuuutt... it's the jet engines/propellers that's driving the plane forward, not the wheels. The wheels are just there to keep friction down to zero, right?

Since the jet engines "function" relative to the ground and NOT the conveyor, it still pushes the plane forward. The conveyor just sort of hits the wheels and nothing happens.

Imagine if you on roller skates and had a jetpack strapped on. Once you go blasting off, it won't matter what conveyor belt stands in your way, since as long as it runs parrallel to you, the conveyor would just affect the tangential velocity of the wheels on your skates.
 
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BobCobb

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Lift has nothing to do with velocity relative to the ground. It has to do with velocity relative to the air, hence flying in the air. Since the velocity of plane relative to the earth(AIR) is zero, it will not take off.

You people are confusing the conveyor belt with the earth. There are not one in the same reference point.
 

Sir_Brizz

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BobCobb said:
Lift has nothing to do with velocity relative to the ground. It has to do with velocity relative to the air, hence flying in the air. Since the velocity of plane relative to the earth(AIR) is zero, it will not take off.

You people are confusing the conveyor belt with the earth. There are not one in the same reference point.
We are not mistaking this. You are still thinking in terms of a motorized vehicle powered by it's base and not by it's top. The wheels HAVE NO FRICTION. There is nothing on them except a handbrake that is obviously not applied (since they are attempting take off). The wheels will be spinning twice as fast as the plane is moving in the opposite direction of the plane. It's quite simple.

The confusion comes from how the stupid riddle is worded, i.e. awfully. The plane is NOT standing still, it is going the same speed as the conveyor belt in the opoosite direction previous to lifting off. It has nothing to do with aerodynamics and everything to do with whether or not the wheels affect the speed of the plane, which they do not. Think of it this way. If this were taking place in a hangar and the plane was hanging from the ceiling with the wheels touching the conveyor belt, the conveyor belt could go whatever speed it wanted, it would not be inhibited by the plane's wheels because they spin forward and backward freely unless the brake is applied.
 

BobCobb

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How is that confusing? :con:

The plane doesn't lift off. The wheels don't even factor into the equation.

Lift off has everything to do with aerodynamics. Nothing to do with wheels.

Seems simple to me.
 

Zxanphorian

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Zxanphorian said:
To be impartial, to truely test this, one must make a massive conveyor belt, with the sensors (to make it move as fast as the plane in the opposite directions), and use a real plane, and to see what happens. :)

I cannot stress this enough. :p
 

Raffi_B

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BobCobb said:
How is that confusing? :con:

The plane doesn't lift off. The wheels don't even factor into the equation.

Lift off has everything to do with aerodynamics. Nothing to do with wheels.

Seems simple to me.
This isn't a physics question... read the problem again. Especially the part where it states that the plane is physically moving. If it's moving, there is lift. Simple as that... no equations needed.
 

shadow_dragon

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BobCobb said:
How is that confusing? :con:

The plane doesn't lift off. The wheels don't even factor into the equation.

Lift off has everything to do with aerodynamics. Nothing to do with wheels.

Seems simple to me.

If a conveyor belt sat their moving as fast as the plane it would not stop the plane from moving, at all, let alone stop it from taking off. You should stop thinking that the conveyor belt is stopping the plane from moving. Nowhere does it say within the riddle even that the conveyor belt is stopping the plane from moving forward at all, only that it move in the opposite direction.

As i said. if the question stated that the plane was "Tied" down, onto the conveyor belt in such a way that it couldn't simply drive off of it, then yeah, sure, it wouldn't get far but it isn't tied down.

Example. Your on a covneyor belt, at all times the belt travels in the opposite direction at the same speed as you. A rocket is attached to your back, your fire it up. How long do you reckon your feet are gonna keep you on the conveyor belt? In teh same way how do you imagine wheels would?
 
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Enfyrneaux

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ROFL :lol:

If the thrust force of the plane's engines is greater than the opposing dynamic friction of the wheels on the conveyor tarmac, then the plane will roll forward relative to the conveyor's superstructure regardless of the conveyor's speed.
 

Otej

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OK first of all there are two forces acting on the wheel, which spins freely
Plane is travelling at the same speed as the belt but in opposite directions
PV = Plane Velocity = a
BV = Belt Velocity = -a
We take the DIFFERENCE to find out the resultant speed in the direction of the plane's travel
PV-BV = a - (-a) = 2a

And now a patronising image to show how the plane moves forward even though the belt moves at the same speed
plane.gif
 
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Sir_Brizz

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Only ones where people don't change their opinion to match that of everyone else once the thread has been figured out :)

And just to be facetious:
BobCobb said:
How is that confusing?

The plane doesn't lift off. The wheels don't even factor into the equation.

Lift off has everything to do with aerodynamics. Nothing to do with wheels.

Seems simple to me.
You're exactly right, the wheels DON'T factor into the equation. For all intents and purposes it's as if the plane isn't even touching the ground or the conveyer belt at all.
 
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