[mike@af]

This sounds like one of those trick questions, where you have to pay attention to the little deatils. I've had a question similar to this before, and this is how I answered it.

A car of (mass=1.5 tons) rides on the deck of a barge (mass=9 tons) floating in calm water. The car is started, driven at 7.5mph relative to the deck for a distance of 45 feet, and then stops.
a. While the car is in motion, how fast is the barge moving in the water?
The barge is not moving at all, it is floating in the water, only the car is moving. However, this is the assumption that the current and wind to not play a factor on the movement of the barge.
b. When the car stops, does the barge also stop?
The barge does not also stop, because it is already stopped. It is floating.
c. After the car stops, how far has the barge moved?
The barge has not moved at all, only the car has moved in the length that it has traveled which was mentioned to be the deck length of 45 feet.

See, the way I see that those are the answers is because when I had a question similar to this the velocity of the barge was not stated, therefore it was assumed that it was stationary and only the objects on the barge were moving. Of course my question dealt with an airplane instead.