A boy is shooting marbles on a flatcar that is itself in uniform motion on a straight, horizontal track. The boy can shoot marbles at a speed of 30 m/s with respect to the flatcar. The speed of the flatcar with respect to the train track rails is 40 m/s. The maximum possible horizontal speed of a marble with respect to the rails is
A) 10 m/s.
B) 30 m/s.
C) 40 m/s.
D) 50 m/s.
E) 70 m/s.

Question

Quizplus · Accepted Answer

The maximum possible horizontal speed of a marble with respect to the rails is when the marble is shot in the same direction as the flatcar's motion. In this case, the speeds add up: 30 m/s (marble with respect to flatcar) + 40 m/s (flatcar with respect to rails) = 70 m/s.

A Boy Is Shooting Marbles on a Flatcar That Is