Single correct option
Two trains of lengths 180 m and 120 m cross each other completely in 10 seconds when running in opposite directions, and in 50 seconds when running in the same direction. What is the speed of the faster train?
- A. 43.2 km/h
- B. 54 km/h
- C. 64.8 km/h
- D. 72 km/h
Show answer and solution
Answer: (C) 64.8 km/h
Distance to be covered in either case = 180 + 120 = 300 m.
Opposite directions: a + b = 300/10 = 30 m/s.
Same direction: a − b = 300/50 = 6 m/s.
So a = 18 m/s and b = 12 m/s. Faster train = 18 × 18/5 = 64.8 km/h.
43.2 km/h is the slower train (12 m/s) — a common trap.
Opposite directions: a + b = 300/10 = 30 m/s.
Same direction: a − b = 300/50 = 6 m/s.
So a = 18 m/s and b = 12 m/s. Faster train = 18 × 18/5 = 64.8 km/h.
43.2 km/h is the slower train (12 m/s) — a common trap.
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