Brainteaser Options

[james]

Here's a question for you:

"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?"

A couple of links discussing it (and some funny rationalizations for peoples incorrect assumptions):
www.kottke.org/06/02/plane-conveyor-belt
www.straightdope.com/columns/060203.html

[womble]

Yeah id guess that close to how it works Em. As long as you can pull harder on the rope than the effect of any friction on the wheels yeah you would move forward. If the rope was the air then this would be flowing over the wings to cause lift.

If this question was following all the laws of physics (which it isnt) then as the plane gave a little thrust (equal to the friction + drag) it would not be moving forward but once the thrust becomes greater than the friction + drag the plane will move forward. The conveyor would end up only doing half the speed of the wheels.
As the plane would be moving forward in this scenario there would be air moving over the wing so the plane would take off.

But in this fictional scenario they seem to have fictional physics as well. "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)".

This suggests that the friction and drag increase at the same rate as the planes thrust so that the thrust never overcomes the friction thus never moves forward.
In this scenario the plane will appear to be not moving thus not having any air over the wings therefore not taking off.

This post has been edited by womble: Feb 28 2006, 10:39 AM