The length of a train is 170 metres and its speed is 63 km/hr. The train…
2025
The length of a train is 170 metres and its speed is 63 km/hr. The train crosses a bridge in 30 seconds. Find the length of the bridge.
- A.
355 mts
- B.
325 mts
- C.
365 mts
- D.
312 mts
Attempted by 9 students.
Show answer & explanation
Correct answer: A
Concept: When a train crosses a stationary object such as a bridge or platform, the total distance covered equals the sum of the train's own length and the length of that object; this distance is covered at the train's speed in the given time, using Distance = Speed × Time.
Application:
Convert the speed to metres per second: 63 km/hr = 63 × 5/18 m/s = 35/2 m/s = 17.5 m/s.
Let the bridge length be x metres. The total distance covered while crossing the bridge is the train's length plus the bridge's length: 170 + x.
The time taken is 30 seconds. Applying Distance = Speed × Time: 170 + x = 17.5 × 30 = 525.
Solving for x: x = 525 − 170 = 355 metres.
Cross-check: Substituting back, the total distance is 170 + 355 = 525 m; at 17.5 m/s this takes 525 / 17.5 = 30 seconds, matching the given crossing time — confirming the bridge length is 355 metres.