The time it takes for a coal train to reach its maximum speed can vary depending on several factors, including the size and weight of the train, the power of the locomotives, the condition of the track, and the gradient of the terrain. However, I can provide a general estimation.
Coal trains are typically very heavy due to the large amount of coal they transport. The acceleration of such a heavy train can be slow compared to lighter passenger trains. It may take several minutes for a coal train to reach its maximum speed, especially if it starts from a stationary position.
On average, it can take anywhere from 5 to 15 minutes for a coal train to accelerate and reach its top speed. However, this is just a rough estimate, and the actual time may vary depending on the specific circumstances mentioned earlier.