Puzzles/Physics puzzles/Train on Circle/Hint

Physics | Physics puzzles | Train on Circle | Hint

A train goes around a circle, the first time with an average velocity of 100 km/h. How fast should the train be when going around the circle again a second time, so that the average velocity over the two loops is 200 km/h?

Hint

 * The obvious answer 300 km/h is wrong.
 * Assume that the circle is 100 km long. How long does the train need for the distance (at 100 km/h)? How long is twice the distance, and how much time is left for the second loop?

Solution