Single correct option
Train A, 180 m long, runs at 54 km/h. It crosses train B, running on a parallel track in the opposite direction, completely in 12 seconds. When both run in the same direction, A crosses B completely in 60 seconds (A being faster). What are the length and speed of train B?
- A. 120 m, 36 km/h
- B. 100 m, 45 km/h
- C. 150 m, 36 km/h
- D. 120 m, 18 km/h
Show answer and solution
Answer: (A) 120 m, 36 km/h
Let total length S = 180 + L and B's speed v m/s. A's speed = 54 × 5/18 = 15 m/s.
Opposite direction: 15 + v = S/12. Same direction: 15 − v = S/60.
Adding: 30 = S(1/12 + 1/60) = S × 6/60 = S/10 → S = 300 m, so L = 120 m.
Then 15 + v = 300/12 = 25 → v = 10 m/s = 36 km/h.
Answer: 120 m, 36 km/h.
Opposite direction: 15 + v = S/12. Same direction: 15 − v = S/60.
Adding: 30 = S(1/12 + 1/60) = S × 6/60 = S/10 → S = 300 m, so L = 120 m.
Then 15 + v = 300/12 = 25 → v = 10 m/s = 36 km/h.
Answer: 120 m, 36 km/h.
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