Let us first concentrate and write down all the information's already given in the question. Based on the information's the answer to the question can be easily deduced. Distance traveled by the train = 225 km Time taken to travel the distance of 225 km = 2.5 hours Then Average speed = Distance traveled/Time taken = 225/2.5 km/hour = 90 km/hour So the average speed of the train is 90 kilometers per hour. The procedure for doing this kind of problem is described and it is the simplest way of solving such problems. I hope you have understood the process and got the answer you were looking for.
Caused by gravity and the roller coaster's position, the potential energy is stored in the roller coaster. For example, this ball is at the top of a hill, where potential energy is at it's highest.