A lucky escape
Two boys walking in the woods decided to take a shortcut through a railroad tunnel. when they had walked two-third of the way through the tunnel, their worst fears were realized. A train was coming from the opposite direction, nearing the tunnel entrance. The boys panicked and each ran for a different end of the tunnel. Both boys ran at the same speed, 10 miles per hour. Each boy escaped the tunnel just at the instant that the train would have squashed them into the rails.
Assuming the trains’ speed was constant, and both boys were capable of instantaneous reaction and acceleration, how fast was the train going ?
I have solved this one. If I had done that earlier, I probably wouldn’t have bothered posting it.