A train of length 210 metres is running at a speed of 54 km/hr. In how much…

To determine the time it takes for the train to completely cross the platform, we need to calculate the total distance covered and then use the speed-time-distance relationship.

Step-by-Step Calculation
Calculate Total Distance:
To completely cross a platform, the train must cover its own length plus the length of the platform.
Total Distance = Train Length + Platform Length
Total Distance = 210 metres + 390 metres = 600 metres

Convert Speed:
The speed is given in km/hr, but the distance is in metres. We need to convert the speed into metres per second (m/s).
Speed in m/s = Speed in km/hr × (5/18)
Speed = 54 × (5/18) = 3 × 5 = 15 m/s

Calculate Time:
Time = Total Distance / Speed
Time = 600 metres / 15 m/s = 40 seconds