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Two trains, each 50 m in length, are travelling on parallel tracks toward one another with speeds of 10 m/s and 15 m/s. How much time will they take to completely cross each other?

1. 5/3 s
2. 4 s
3. 2 s
4. 6 s

Correct answer: 4 s

Solution

Trains approach, so relative speed = 10+15 = 25 m/s. To fully cross, the relative displacement = sum of lengths = 50+50 = 100 m. Time = 100/25 = 4 s.

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