How long does it take for a train to pass a 400 m long tunnel if the train length is 100 m and the speed is 36 km / h.

Given:

L1 = 400 meters – tunnel length;

L2 = 100 meters – train length;

v = 36 kilometers per hour = 10 meters per second – train speed.

It is required to determine t (seconds) – how long it takes for the train to pass the tunnel.

The train will pass the tunnel completely when its last carriage leaves the tunnel. Therefore, the train will have to travel a distance equal to:

S = L1 + L2 = 400 + 100 = 500 meters.

Then the time will be equal to:

t = S / v = 500/10 = 50 seconds.

Answer: the train will pass the tunnel in a time equal to 50 seconds.