The energy would come from the trolley.
Has the trolley come to a complete halt, or even showed down? If not, then either no energy has been transferred to the people and they just flop out, or we've just invented perpetual motion.
Has the trolley come to a complete halt, or even showed down? If not, then either no energy has been transferred to the people and they just flop out, or we've just invented perpetual motion.