Introduction: Problems on Trains

When two trains are going in the same direction, then their relative speed is the difference between the two speeds.

When two trains are moving in the opposite direction, then their relative speed is the sum of the two speeds.

When a train crosses a stationary man/ pole/ lamp post/ sign post- in all these cases, the object which the train crosses is stationary and the distance travelled is the length of the train.

When it crosses a platform/ bridge- in these cases, the object which the train crosses is stationary and the distance travelled is the length of the train and the length of the object.

When two trains are moving in same direction, then their speed will be subtracted.

When two trains are moving in opposite directions, then their speed will be added.

In both the above cases, the total distance is the sum of the length of both the trains.

When a train crosses a car/ bicycle/ a mobile man- in these cases, the relative speed between the train and the object is taken depending upon the direction of the movement of the other object relative to the train- and the distance traveled is the length of the train.

Basic formula to remember:

1. how to convert “x km/hr” into m/s is
x km/hr = x*5/18 m/s
how to convert “x m/s” into km/hr is
x m/s = x*18/5 km/hr

2. Two trains in the Same direction (one train with x km/hr speed, second train with y km/hr speed) then total speed = (x+y) km/hr
Two trains in the opposite direction (one train with x km/hr speed, second train with y km/hr speed) then total speed = (x-y) km/hr

3. Speed = Distance/time