Two students 8 meters apart are holding a stretched, coiled spring between them. One student sends a pulse down the string, and they observe it takes 4 seconds for the pulse to go from one e=nd of the spring to the other and then back to it's starting point what is the speed of the pulse on the string

The man of mass m1 and the woman of mass m2 are standing on opposite ends of the platform of mass m0 which moves with negligible friction and is initially at rest with s = 0. the man and woman begin to approach each other. derive an expression for the displacement s of the platform when the two meet in terms of the displacement x1 of the man relative to the platform.