If the black hand of the duplex gauge indicates 45 pounds when the controller handle of a train is moved to an "ON" position, what will the train do?

When the black hand of the duplex gauge indicates 45 pounds while the controller handle of the train is moved to the "ON" position, this indicates a relatively low amount of power being applied to the train's traction system. In train operation, the duplex gauge measures the amount of tractive effort or power that the locomotive is providing to move the train.

A reading of 45 pounds suggests that the train is receiving a level of power sufficient to initiate motion but not enough to provide a rapid acceleration. This lower level of tractive power will result in a gradual increase in speed rather than a quick burst of acceleration, making the option that states the train will accelerate very slowly the correct choice.

In contrast, readings that indicate much higher tractive effort would lead to quicker acceleration, while insufficient power would result in the train either remaining stationary or decelerating. Therefore, with 45 pounds on the gauge, the train's response aligns with a slow and controlled acceleration, reflecting sound operations within the constraints of the power indicated.