Two trains 400 m and 350 m long are running on the parallel track at the rate…

CONCEPT:

When two bodies travel in the same direction, their relative speed equals the difference of their individual speeds. Two trains finish crossing each other exactly when the distance covered at this relative speed equals the sum of their lengths, so crossing time = (sum of lengths) ÷ (relative speed).

GIVEN:

• Length of Train 1 (L1) = 400 m, Length of Train 2 (L2) = 350 m

• Speed of Train 1 (S1) = 80 km/h, Speed of Train 2 (S2) = 90 km/h, both moving in the same direction

APPLICATION:

1. Relative speed = S2 − S1 = 90 − 80 = 10 km/h (same-direction motion, so speeds are subtracted).

2. Convert to m/s: 10 km/h = 10 × (5 ÷ 18) = 50/18 m/s.

3. Total distance to be covered = L1 + L2 = 400 + 350 = 750 m.

4. Crossing time = distance ÷ relative speed = 750 ÷ (50/18) = 750 × (18/50) = 270 sec.

CROSS-CHECK:

At 50/18 m/s (≈ 2.78 m/s), covering 750 m takes about 750 ÷ 2.78 ≈ 270 s, confirming the result independently.