Imagine that a passenger is walking toward the back of a train as the train is leaving the station. Why would this person’s description of their motion differ from that of an observer standing on the station platform?

Suppose that three astronomical objects, 1, 2, and 3 are observed to lie on a line, and the distance from object 1 to object 3 is d. object 1 has four times the mass of object 3, and seven times the mass of object 2. find the distance between objects 1 and 2 for which the net force on object 2 is zero.