A freight train left the station, traveling at a speed of V1 = 36 km / h, after 30 minutes. an express train departed

A freight train left the station, traveling at a speed of V1 = 36 km / h, after 30 minutes. an express train departed in the same direction, the speed of which was V2 = 72 km / h. How long after the goods train leaves and at what distance will the express train catch up with the goods train?

Displacement at a known speed and time is calculated by the formula: S = v * t.

The freight train managed to cover the distance in half an hour:

S = 36 km / h * 0.5 h = 18 km and will move on, therefore, the equation of its motion will be:

S1 = 18 + v * t = 18 + 36 * t.

The equation of movement of the express will be as follows:

S2 = 72 * t.

Therefore, we need to find the moment in time when S1 = S2

72 * t = 18 + 36 * t,

36 * t = 18,

t = 0.5 h.

t is the MOVEMENT time of the freight train and express, but the express left when the freight train was already 0.5 hours on the way, so 0.5 hours must be added to the time t to find out how long it will take for the express train to catch up with the freight train.

Answer: the express train will catch up with the freight train 1 hour after the last one leaves.