A Freight Train Consists of an Engine and Several Identical

Multiple Choice

A freight train consists of an engine and several identical cars on a straight, level track. Which of the following statements is true?

A) If the train is moving at constant speed, the engine must be pulling with a force greater than the train's weight.
B) If the train is moving at constant speed, the engine's pull on the first car must exceed that car's backward pull on the engine.
C) If the train is coasting, its inertia makes it slow down and eventually stop.
D) If the train is moving at constant speed, the engine's pull must be equal to the force of friction.