A train 130 meters long travelling at 54 km/hr crosses the bridge in 30 sec.…
2017
A train 130 meters long travelling at 54 km/hr crosses the bridge in 30 sec. Then the length of the bridge is:
Answer: A. 320 meters — ConceptWhen a train crosses a bridge (or platform), the train must travel a distance equal to its OWN length PLUS the length of the bridge, because the rear…
- A.
320 meters
- B.
350 meters
- C.
325 meters
- D.
375 meters
Attempted by 5 students.
Show answer & explanation
Correct answer: A
Concept
When a train crosses a bridge (or platform), the train must travel a distance equal to its OWN length PLUS the length of the bridge, because the rear of the train only clears the far end after moving that combined distance. Distance = speed x time, and a speed in km/hr is converted to m/s by multiplying by 5/18.
Application
Convert the speed: 54 km/hr = 54 x 5/18 = 15 m/s.
Total distance covered while crossing = speed x time = 15 m/s x 30 s = 450 m.
This total distance equals train length + bridge length, so bridge length = 450 - 130 = 320 m.
Cross-check
Add the bridge length back to the train length: 320 + 130 = 450 m. At 15 m/s, covering 450 m takes 450 / 15 = 30 s, which matches the given time. So the bridge is 320 m long.