To determine the time it takes for the train to cross the bridge, we need to calculate the relative speed between the train and the bridge.
The train's speed is given as 10 km/hour. Since the length of the train is 1 km, it will take 1/10 hours (or 6 minutes) for the train to completely pass any given point.
Now, when the train is crossing the bridge, it covers a distance equal to the length of the bridge, which is also 1 km. Therefore, the time it takes for the train to cross the bridge will be the same as the time it takes to cross a 1 km distance at a speed of 10 km/hour.
Hence, the train will take 6 minutes (or 0.1 hours) to cross the 1 km long bridge.