A passenger travels in a train with a speed of 80 km / h. A 1 km long freight train is moving towards

A passenger travels in a train with a speed of 80 km / h. A 1 km long freight train is moving towards this train at a speed of 40 km / h. How long will a freight train pass by a passenger?

Given:

v1 = 80 km / h = 22.2 m / s – the speed of the passenger train;

v2 = 40 km / h = 11.1 m / s – the speed of the freight train;

L = 1 kilometer = 1000 meters – the length of the freight train.

It is required to determine t (hour) – how long the freight train will move past the passenger.

Since, according to the condition of the problem, both trains are moving towards each other, then the speed of the passenger train relative to the freight train will be equal to:

v = v1 + v2 = 22.2 + 11.1 = 33.3 meters per second.

Then the time will be equal to:

t = L / v = 1000 / 33.3 = 30 seconds.

Answer: a freight train will move past the passenger for 30 seconds.