During the first half of the journey, the train moved at a speed of 1.5 times more than the second

During the first half of the journey, the train moved at a speed of 1.5 times more than the second half of the journey. What is the speed in each section, if the average speed is 12 m / s.

Initial data: S1 = S2; V1 (speed in the first half of the trip) = 1.5V2 (speed in the second half of the trip); Vav. (average train speed) = 12 m / s.

1) Speed on the second half of the journey: Vav. = S / t = S / (t1 + t2) = S / (S / 2V1 + S / 2V2) = 1 / (1 / 2V1 + 1 / 3V1) = 1 / (5 / 6V1) = 6V1 / 5 = 12 , whence V1 = 12 * 5/6 = 10 m / s.

2) Speed on the first half of the journey: V1 = 1.5V2 = 1.5 * 10 = 15 m / s.

Answer: The speed in the first section is 15 m / s; the speed in the second section is 10 m / s.