From the Sir Isaac Newton contest: A 1.0*10^3 kg plane is tryin to make a forced landing on the deck of a 2.0*10^3 kg barge at rest on the surface of a clam sea. THe only frictional force to consider is between the plane's wheels and the deck, this braking force is constant and is equal to one quarter of the plane's weight. What must the minimum length of the barge be for the plane to stop safely on deck, if the plane touches down just at the rear end of the deck with a velocity of 5.0*10^1m/s towards the front of the barge? Sorry, I don't quite understand this question. When the plane touches down, the barge will move as well, due to the frictional force. Then, how should I understand the motion of the plane? : should the plane be moving ahead at 51m/s, with deceleration determined by the braking force.... or do we also have to take into consideration of the barge's motion as well? Please, does someone have a solution for the problem? Thank you!