Quick Concept Summary
Train questions are time-speed-distance questions with one extra idea: the moving object has length. First decide what distance must be covered, then divide by speed.
Distances to Use
| Situation | Distance Covered |
|---|---|
| Crossing a pole/person | Train length |
| Crossing a platform/bridge | Train length + platform length |
| Two trains crossing | Sum of train lengths |
Worked Examples
Example 1: Pole
A 180 m train runs at 54 km/h. Time to cross a pole?
54 km/h = 15 m/s
Time = 180/15 = 12 seconds
Example 2: Platform
A 150 m train crosses a 250 m platform at 20 m/s.
Distance = 150 + 250 = 400 m
Time = 400/20 = 20 seconds
Example 3: Two trains
Two trains of 120 m and 180 m move opposite ways at 36 km/h and 54 km/h.
Relative speed = 10 + 15 = 25 m/s
Distance = 300 m
Time = 300/25 = 12 seconds
Practice Questions
1. A 240 m train at 72 km/h crosses a pole. Find time. 2. A 100 m train crosses a 200 m platform in 15 seconds. Find speed. 3. Two trains 150 m each move in opposite directions at 45 km/h and 63 km/h. Find crossing time. 4. Two trains move in same direction at 70 km/h and 50 km/h. Find relative speed. 5. A train crosses a man in 8 seconds and a platform in 20 seconds. What extra information is needed to find platform length?
Common Mistakes
- Forgetting to convert km/h into m/s
- Using platform length only
- Using wrong relative speed
Revision Checklist
- [ ] Pole vs platform distance
- [ ] Same vs opposite direction
- [ ] km/h to m/s conversion