Airplane on a Conveyor conundrum

[Slugsie]

This is tickling me. I'm supposed to be working.

Yup, me too. Luckily the guy I need to speak to to get the information that I need to get on with my work is out of the office today.

[Slugsie]

If the conveyor is moving, it cannot be be going at the same speed as the ground!!

Lets, just for the moment, measure the speed of everything, relative to the ground.
to start, the plane is not moving, the belt isn't moving, the engines are not even running.
The engines start, the plane moves, lets say North.
the belt moves south.
the plane is now doing 10mph north. the belt is going 10mph south. so the wheels are doing 20mph.
The plane accelerates, to say 200mph - it's take off speed. the belt is now going 200mph the other way. the wheels are doing 400mph.
the plane takes off because the plane is moving relative to the ground and, as according to the original question, the is no wind, it is moving through the air at 200mph so it will take off.
there is absolutely nothing about the wheels doing 400 mph or the belts movements that can prevent the plane flying

A very succinct description.

[dieselboy]

Nope, doesn't say that at all. It says that it matches the speed, but goes backwards. That is not the same as 'moves relative to'.

yes
of course its going to be relative.
its going the same speed as the plane all the time! but only it has a minus symbol in front of it

*sigh*

[Slugsie]

yes
of course its going to be relative.
its going the same speed as the plane all the time! but only it has a minus symbol in front of it

*sigh*

But given that the planes speed is measure relative to the ground, the conveyors speed has also to be measured relative to the ground. Therefore the relative speeds between the plane and the conveyor becomes 20mph if they're both moving at 10mph (one forward, one backward).

**sigh**

[dieselboy]

A very succinct description.

yes but it has nothing to do with this question.

and why measure everything the same speed as the ground now? thats not what it says in the question..

if this were the case, then the plane wouldnt take off at all.
the plane wouldnt take off because there would be no wind to lift the wings, this is because the plane doesnt move. this is because the conveyor is goin one way at x speed, and the thrust is enough to keep it stationary to the ground.
this explanation has nothing to do with this at all

[nero279]

Ignore the ground and the conveyor, what happens?

[dieselboy]

But given that the planes speed is measure relative to the ground, the conveyors speed has also to be measured relative to the ground.
lol they are both 0mph

Therefore the relative speeds between the plane and the conveyor becomes 20mph if they're both moving at 10mph (one forward, one backward).

no, if this were to happen then you are saying that when you drive away from tescos at 10mph, that tescos is also moving away from you at 10mph = you are moving away from each other at 20mph
but of course this doesnt happen, because tescos dont have wheels. unless its a home delivery but lets not go there

**sigh**

now this should make sense

[Sancho]

yes but it has nothing to do with this question.

and why measure everything the same speed as the ground now? thats not what it says in the question..

if this were the case, then the plane wouldnt take off at all.
the plane wouldnt take off because there would be no wind to lift the wings, this is because the plane doesnt move. this is because the conveyor is goin one way at x speed, and the thrust is enough to keep it stationary to the ground.
this explanation has nothing to do with this at all

I can't believe it took you 380 posts to understand the question and then you still got the answer wrong. I can't stop laughing. That's genius.

[Slugsie]

now this should make sense

Nope, that is not what I am saying at all.

[dieselboy]

I can't believe it took you 380 posts to understand the question and then you still got the answer wrong. I can't stop laughing. That's genius.

what are you smoking

the end of the day, the answer for the question in post 1 is:
THE PLANE WILL TAKE OFF.
the reason is that the equasion would mean that the conveyor and the ground are both going the same speed. no ifs no buts blah blah.

if, however, the conveyor speed was always the opposite of the planes but it was measured by its speed from the ground (this is not the question) then the outcome of this is that:
THE PLANE WILL NOT TAKE OFF
this is because the conveyor will always produce the exactly the same ammount (equal) drag to the thrust that the jets produce.

this is why, i was wrong at the fist post i wrote, because i mis read the question, and now i understand the question, i have proved an answer, but no one understands

this is why sancho is wrong, and is trying to ridicule me

and this is why chillitt and slugsie and everyone else that agreed with them is in fact correct..
but no one understands why.

[Slugsie]

yes but it has nothing to do with this question.

and why measure everything the same speed as the ground now? thats not what it says in the question..

if this were the case, then the plane wouldnt take off at all.
the plane wouldnt take off because there would be no wind to lift the wings, this is because the plane doesnt move. this is because the conveyor is goin one way at x speed, and the thrust is enough to keep it stationary to the ground.
this explanation has nothing to do with this at all

Erm, yes, that is exactly what it says in the question. And yes, the airplane does take off.

[nero279]

12 posts to go

[Slugsie]

no, if this were to happen then you are saying that when you drive away from tescos at 10mph, that tescos is also moving away from you at 10mph = you are moving away from each other at 20mph

Nope, if you do it that way then you are measuring your speed relative to the ground, and tescos speed relative to you. That has never been the case with this question.

It would be more accurate to say you are driving down the northbound carriage way of the M6 at 70mph. The copper in the southbound carriage way is also doing 70mph. You pass each other at 140mph. Do you have even a slight worry that you'll be done for speed at 140mph?

[Sancho]

what are you smoking

Believe it or not, I just flew back in from Thailand last night so I've got a bit of jet lag that might be causing erratic behaviour....

[Sancho]

It would be more accurate to say you are driving down the northbound carriage way of the M6 at 70mph. The copper in the southbound carriage way is also doing 70mph. You pass each other at 140mph. Do you have even a slight worry that you'll be done for speed at 140mph?

How fast is Tescos going?