Multiple choice

An express train 130 m long moving at a speed of 80 km/hr crosses a train 120 m long coming from opposite direction in 5 sec. Find the speed of the second train.

  1. 140 km/hr

  2. 130 km/hr

  3. 110 km/hr

  4. 100 km/hr
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D Correct answer
Explanation

Relative speed = Total distance / Time = (130 + 120) / 5 = 250 / 5 = 50 m/s. 50 m/s = 50 * 18/5 = 180 km/hr. Since they are moving in opposite directions, relative speed = v1 + v2. 180 = 80 + v2, so v2 = 100 km/hr.

AI explanation

The total distance covered is the sum of the lengths of the two trains, which is 130 m plus 120 m, giving 250 m. The relative speed is distance divided by time, so 250 m divided by 5 sec gives a relative speed of 50 m/s, which converts to 180 km/hr. Since they are moving in opposite directions, the relative speed is the sum of their speeds. Subtracting the first train's speed of 80 km/hr from the relative speed of 180 km/hr leaves the second train's speed at 100 km/hr.

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