Final answer:
The most serious consequence to the equipment if a train is tripped at about 18 miles per hour will likely be derailment, causing substantial damage to the train and tracks.
Step-by-step explanation:
If a train is tripped while running at about 18 miles per hour, the most serious consequence to the equipment will probably be derailment. The concept of a train being 'tripped' likely refers to an incident where the train's wheels lose contact with the rails, or an obstruction causes the train to leave its intended path. At 18 miles per hour, the kinetic energy involved is significant and could result in substantial damage to both the train and rails.
Moreover, there might be issues related to the stability and alignment of the tracks post-incident which may affect future operations, indicating the importance of maintaining rail infrastructure to prevent such occurrences.