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Old 03-06-2006, 11:08 AM
bup bup is offline
Join Date: Sep 1999
Location: glenview,il,usa
Posts: 11,905
Originally Posted by jere7my
I think it's much more likely that the question is asking about the plane's speed relative to the ground. It doesn't make sense to me to say the speed of the belt is "exactly the same" as the speed of the plane when the speed of the belt would have to be much much faster than the plane's top speed could ever be (~600 mph for a 747). The belt is no longer matching the plane's speed, in this thought experiment; it's moving fast enough that friction prevents the plane from moving, which is not the same thing.
I see at as asking a question which contains a paradox, like Cecil's first column says.

It's like the question, "A car travels 50 miles of a hundred mile trip at 30 mph. How fast does it need to go for the last fifty miles to average 60 mph?"

Implicit in the question is an impossibility.

I guess a more accurate answer would be 'mu,' but I'm more inclined to say you can't make a treadmill that stops a plane's forward movement, therefore the plane takes off.