train and spring problem problem: At the train station, you notice a large horizontal spring at the end of the track where the train comes in. This is a safety device to stop the train so that it will not go plowing through the station if the engineer misjudges the stopping distance. While waiting, you wonder what would be the fastest train that the spring could stop by being fully compressed, 4.2 feet. You assume that in order to keep the passengers safe when the spring stops the train, the maximum stopping acceleration of the train, caused by the spring, is g/2. You are not sure about the train's weight, so you make a guess that a train might have a mass of 0.5 million kilograms. For the purpose of getting your answer, you assume that all frictional forces are negligible. What is the maximum train speed? i thought it would be a simple problem of just setting the kinetic energy = to the work done by the force of the spring 1/2 m^2 V = Force*mass*distance 4.2ft=1.28m g/2=4.9 and i got v = 3.542 m/s.... but it's wrong... anyone know what i did wrong?