"Darrell S" wrote in message
news:rT6Ff.24873$jR.14387@fed1read01...
[...] For a car the situation would be completely different since it
produces forward motion by the tires which contact the moving conveyer
belt. The car wouldn't move at all.

It might. As "Doug" points out, the presentation is ambiguous as to the
reference point for the speed of the vehicle. If one uses the ground (and
stationary portions of the treadmill) as a reference, then the car would
move, just as the airplane does (it would have to in order to comply with
the description given in the problem), and the car's speedometer would
register a speed twice its actual speed relative to that reference.

Pete