Problems on Trains

5 min

Master relative speed, crossing objects and trains easily

The Golden Rule

When a train crosses a pole or person, total distance is the train's length. When it crosses a platform, bridge or another train, total distance is the sum of both lengths.

Why This Topic Matters

Guaranteed 1 to 2 questions in SSC, Railway and Defence exams.
Tests fundamental concepts of relative speed and unit conversion.
Builds a strong base for time, speed and distance chapters.

Smart Memory Hooks

Km/h to m/s: Multiply by 5/18. Think 'Small unit, small number on top'.
Same Direction: Relative Speed = Difference (S1 - S2).
Opposite Direction: Relative Speed = Sum (S1 + S2).

Crossing Scenarios Summary

Object Crossed	Distance (D)	Speed (S)
Pole / Man	Length of Train	Speed of Train
Platform / Bridge	Train + Platform	Speed of Train
Opposite Train	Train 1 + Train 2	Sum (S1 + S2)
Same Direction Train	Train 1 + Train 2	Diff (S1 - S2)

Visualizing Crossing Types

POLE

(Zero Length Object)

Zero Length Object

Train crosses a standing pole.

PLATFORM

(Stationary Length)

Stationary Length

Train crosses a 200m platform.

OPPOSITE

(Speeds Add Up)

Speeds Add Up

Two trains cross head-on.

SAME DIR

(Speeds Subtract)

Speeds Subtract

Faster train overtakes slower one.

Common Exam Traps

Forgetting to add platform lengthAlways add platform + train length

Students often divide train length alone by speed when crossing a platform.

Mixing km/h and meters directlyConvert km/h to m/s using 5/18

Units must always match before applying distance equals speed into time.

Adding speeds in same directionSubtract speeds (S1 - S2)

In the same direction, relative speed is always the difference between speeds.

Test Your Readiness

Q1.A 120m long train running at 54 km/h crosses a pole in how many seconds?

Q2.Two trains of lengths 150m and 250m run towards each other at 40 km/h and 32 km/h. Time taken to cross each other?

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