The length of the bridge, which a train 130 metres long and travelling at 45 km/hr can cross in 30 seconds, is:

Step 1: Understand the given data

• Length of the train = 130 meters
• Speed of the train = 45 km/h
• Time taken to cross the bridge = 30 seconds

Step 2: Convert speed to m/s

To convert km/h to m/s, multiply by 5/18:

Speed = 45 × (5/18) = 12.5 m/s

Step 3: Calculate total distance covered in 30 seconds

Distance = Speed × Time = 12.5 × 30 = 375 meters

Step 4: Calculate the length of the bridge

Total distance covered = Length of train + Length of bridge

375 = 130 + Length of bridge
Length of bridge = 375 - 130 = 245 meters

Answer: 245 meters

The train will cross a bridge of 245 meters in 30 seconds.

This question demonstrates the use of basic speed–distance–time formula, and how the total distance covered when a train crosses a bridge includes both the train's length and the bridge's length.