The length of a train is 170 metres and its speed is 63 km/hr. The train…

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:

1. Convert the speed to metres per second: 63 km/hr = 63 × 5/18 m/s = 35/2 m/s = 17.5 m/s.

2. 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.

3. The time taken is 30 seconds. Applying Distance = Speed × Time: 170 + x = 17.5 × 30 = 525.

4. 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.