A train 360 m long is running at a speed of 45 km/hr. In what time will it pass a bridge 140 m long?

Step 1: Understand the given information

• Length of train = 360 meters
• Length of bridge = 140 meters
• Total distance to cover = 360 + 140 = 500 meters
• Speed of train = 45 km/hr

Step 2: Convert the speed to meters per second

1 km/h = 5/18 m/s

So, 45 km/h = 45 × 5/18 = 12.5 m/s

Step 3: Use the formula: Time = Distance / Speed

Time = 500 / 12.5 = 40 seconds

Answer: 40 seconds

The train will take 40 seconds to cross the bridge completely.

This question involves the concept of relative motion where the train has to cover both its own length and the bridge’s length. Converting the speed into m/s ensures unit consistency while applying the distance-speed-time formula.