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]

My answer was in 2 parts, one being with real physics applied to what would happen and the other was applying real physics to make the fictional question actually happen.

The increase in friction is what would have to happen for the fictional scenario of the belt being able to keep up with the wheels. (trying to apply some basic physics to a fictional scenario to make it happen)
If thrust is greater than friction then you have forward movement. Therefore for the belt to keep the plane at standstill as the plane gave more thrust something else would have to increase as well,(velocity wouldnt do it on its own as the wheel would freewheel (no friction) So we have to apply friction between the wheels and the belt and this friction would have to increase at the same rate as the thrust increased. with that we get friction equals thrust and no movement.


You could look at it another way in that the engines are so small that they can only produce enough thrust to match friction thus it would appear not to move. If this was the case then the plane wouldnt take off even if it was on a normal runway.

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