Critical thinking puzzle.

[Skepticus Rex]

ah! i've suddenly realised what i was doing wrong.

the way i went through what was happening was this:
1st premise: when the plane is not powered, the conveyor will move the whole thing backward (i still think that's true, although some people seemed to disagree).
2nd premise: when the engine is on, it will push the wheels forwards over the belt.

both of these are true - on their own.
my mistake was to put the two together (hence the cancelling out of forces). i thought of the plane moving backward as a given, which it isn't unless the belt is exerting an attractive force on the wheels.
when the plane isn't moving, gravity on the plane has the same affect as a force attracting the wheels (well, the entire plane) to the belt. that is why it will move backward with the belt, but when the force of the engine has overcome the friction with the belt, then the plane, and therefore the force attracting the wheels to the belt, is moved forwards.
i was thinking of the wheels being attracted to the belt all the time, as something seperate from the gravity. if there was such a force, then the plane would stay still. but there isn't...

i apologise profusely for dragging this thing out, i got really mixed up there.
yes, the plane would be able to take off, because it will move against the belt just like a runway (although the force of the belts movement will not have no affect, it would increase the friction between the wheels and the belt when the plane was trying to move, so more energy would be needed to overcome it.), which is exactly what you were trying to tell me vbloke, i'm sorry.

[median]

Now if you had a plane with a massive frictional adhesion to the conveyor (huge wheels) and a conveyor belt with a high gearing then this might be a different matter ???

But let's not go there eh

[wollery]

1st premise: when the plane is not powered, the conveyor will move the whole thing backward (i still think that's true, although some people seemed to disagree).

Not wishing to be overly pedantic (yeah right, ed.), but since the wheels are free spinning the plane might not move backwards at the same speed as the conveyer belt, unless the belt was accelerated quite slowly.

Inertia's a bitch!

[Skepticus Rex]

Not wishing to be overly pedantic (yeah right, ed.), but since the wheels are free spinning the plane might not move backwards at the same speed as the conveyer belt, unless the belt was accelerated quite slowly.

Inertia's a bitch!

the wheels arn't free spinning when the planes engine isn't running, because the entire weight of the plane is resting on them (unless it's a plane where the tail touches the ground when it's stationary, in which case the conveyor belt would move it whether the wheels are free spinning or not).

[wollery]

the wheels arn't free spinning when the planes engine isn't running, because the entire weight of the plane is resting on them (unless it's a plane where the tail touches the ground when it's stationary, in which case the conveyor belt would move it whether the wheels are free spinning or not).

If the wheels aren't free spinning then the plane would have real difficulty taking off!

But to answer your point properly, I did say that the plane would move backwards at the same speed as the conveyor if it was accelerated slowly!

[vbloke]

Mythbusters had a go at the plane on a conveyor belt problem.

http://mythbustersresults.com/episode97