Two trains of lengths 120 m and 90 m are running with a speed of 80 km/h and 55 km/h respectively towards each other on parallel lines. If they are 90 m apart, after how many seconds they will cross each other?
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5.6 second
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7.2 second
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8 second
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9 second
C
Correct answer
Explanation
When trains move toward each other, add their speeds to get relative speed: 80 + 55 = 135 km/h = 135 × 5/18 = 37.5 m/s. Total distance to cross = sum of train lengths + initial gap = 120 + 90 + 90 = 300 m. Time = distance/speed = 300/37.5 = 8 seconds. Option A (5.6s) forgets to add train lengths; Option B (7.2s) uses wrong speed conversion; Option D (9s) miscalculates the distance.