Skill's weekend teaser

[Skill Leverage]

Imagine a 747 sitting on a very large conveyor belt. The belt has the same dimensions as a runway at an airport*, and is set up to exactly match the speed of the plane's wheels, moving in the opposite direction. What will happen?

Same rules as before please; no explanation for a little while, no Googling, everyonerich you are banned from participating**.

SL

*To save confusion, the conveyor belt is the same length as the distance required for a 747 to take off from a normal runway; the frictional co-efficient of runway tarmac and the belt are identical, all other variables such as wind and atmospheric conditions can be ignored.
**I'm just kidding (but not really).

 

[megamuel]

Easy (I said that last time lol!).

Sam.

 

[Skill Leverage]

Lol yeah and you're wrong again this time! I won't explain yet though so PM me if you want to know why

 

[megamuel]

Damn! Knew it would be wrong! I'll wait and see what everyone else says!

Sam.

 

[westernforce]

Is the plane tethered with some sort of rope, keeping it in a "somewhat" fixed position?

 

[Skill Leverage]

Is the plane tethered with some sort of rope, keeping it in a "somewhat" fixed position?

er, no. This isn't a trick question.

 

[Hotch]

Next!

Gotta come up with something harder skill!

(presume I'm right at least, being in the minority usually suggests it)

 

[Skill Leverage]

(presume I'm right at least, being in the minority usually suggests it)

Ha that seems to be a pretty good algo for taking part in T2W polls

 

[arabianights]

this is so 2007 man

even been on mythbusters!

 

[Skill Leverage]

Has it? Did they have a runway-sized conveyor belt and everything, or did they use a model (boring)

 

[Aspire]

Looks like I'm the only one so far to say the plane will run out of runway before it takes off. Not sure if that's a good sign or not.

 

[TheBramble]

How can it run out of runway if it's on a conveyor?

 

[Aspire]

Skill, can I explain myself? No one else has given any reasons and I don't want to influence your poll with my fuzzy logic.

 

[Skill Leverage]

We're on page 2 now so I guess you can give your reasoning.

TheBramble that's a bit of a vague statement; are you saying it couldn't take off either?

 

[Aspire]

Ok.

The Conveyor moves at the same speed as the planes wheels.

They both start stationary, then the plane starts its engines. To begin with the conveyor is stationary because the planes wheels are stationary so the thrust of the engines pushes the plane forward.

The conveyor then reacts and goes the other way, slowing the plane down but before it can stop it completely the speed of the plane and hence it's wheels has dropped and so the conveyor slows down too.

This then allows the plane's engines to thrust it forward again. The planes speeds up - the conveyor speeds up - the plane slows down etc etc.

So I reckon how the plane moves depends on how quickly it accelerates and how quickly the conveyor accelerates and reacts but in short the plane will move forward but the conveyor's reactions will stop it taking off before the end of the runway.

That's my take on it anyway.

 

[Skill Leverage]

You're forgetting something about the mechanics of the aircraft, which is something 90% of people do at first, so you're in good company.

 

[Skill Leverage]

You touch on it exactly in your explanation, but you miss its purpose. I won't highlight it just yet, but think about how a plane is able to fly and then look at the problem again.

 

[Aspire]

Not the fact that the plane is driven by it's engines thrust rather than the speed of it's wheels then.... Well, I'm stumped.

 

[Skill Leverage]

Well that's exactly the point. So why would it run out of runway?

 

[Aspire]

Ah... The plane moves relative to the air, not the runway, so the conveyor won't be able to slow the plane down, just make it's wheels spin super fast.. so the plane takes off normally.