Important Concepts and Formulas
- Time taken to cross a man or pole –
Length of Train / Speed of Train
- Time taken to cross a Platform –
Length of (Train + platform) to Speed of Train
- Time taken to cross a Bridge –
Length of (Train + platform) to Speed of Train
- When two trains move towards each other, then the time taken to cross each other is –
Ratio of Sum of Lengths of both Trains to the Sum of their Speeds
- When two trains are moving in the same direction, then the time taken to cross each other is –
Ratio of Sum of Lengths of both Trains to the Difference of their Speeds
Relative Speeds
- When two trains @ x km/hr and y km/hr respectively move towards each other-
Relative Speed = (x + y) km/hr
- When two trains @ x km/hr and y km/hr respectively move in the same direction-
Relative Speed = (x – y) km/hr
Example-
Q- 1> A train 150 meters long is running with a speed of 68 kmph. At what time will it pass a man who is running at 8 km/hr in the same direction in which the train is moving?
Solution-
Relative Speed – (68 – 8) kmph = 60 kmph
Speed in m/sec = 60 × 5/18 = (50/3) m/sec
Now, Time taken by the train to cross the man is the time taken by the train to cover 150-meter distances.
So, Time = (Distance / Speed) = (150 × 3)/50 = 9 seconds (Answer)