I found the following question on an standardized test, and was debating with some friends what the answer would be:
A car of mass M is travelling with a constant velocity through a plane in which friction is non-existent. An object of mass m (
m = M/3) that is falling perpendicularly to the car lands inside of it. How will the velocity of the car be affected?
This illustration can help explain the problem.
My initial thought was that the velocity would be the same, given that friction is non-existent and that the momentum of the falling object is perpendicular to that of the car. However, some friends suggested that, since the mass of the car increases, the velocity should decrease.