The answer is it depends. It depends on the engine's size, the coal's grade, the terrain's steepness, and how much tonnage the locomotive is pulling. Temperature was also a factor. If it was winter, passenger trains were heated by steam the locomotive generated, making them less efficient at pulling.
I found some comments on the trusty internet from a former locomotive engineer for Union Pacific who said coal-powered trains typically made stops every hundred miles or so to load up with more coal. Of course, that depends, too. It depends on the size of the tender and all the other “depends” listed above. The same engineer noted that trains had to stop twice as often to take on water, which was just as important as coal.
And what about the guy shoveling the coal? Did he ever get a break? Not really. You didn’t want to put too much coal on at once or it wouldn’t burn efficiently. Experienced firemen would lift six to nine shovels full and dump them into the burner.
Now that I’ve given you almost no information you can really count on, I’m going to trust that some of the train fanatics who read these posts will set me straight. I’m looking at you, John Wood!