<p>Oh, good point. The runway would move forward, and we would just have a very heavy airplane.</p>
<p>You see, the problem I’m trying to fix is a possible logical flaw in the problem statement. In saying “the treadmill runs in the opposite direction at the same speed the plane is moving”, the problem assumes a certain situation is possible. While this happens to be true, there should be a way of stipulating it without tying together the velocities like that. Or at least, so it seems to me.</p>