A point mass starts moving in a straight line with a constant acceleration a. At a time t1 after the beginning of motion, the acceleration changes sign, remaining the same in magnitude. Determine the time t from the beginning of motion in which the point mass returns to the initial position. For of the distance between two stations, a train is uniformly accelerated and for of the distance, it is uniformly retarded. It starts from rest at one station and comes to rest at another. Find the ratio of its maximum velocity to its average velocity.