+37146 The fron of the train enters tunnel at 120 km/hr and 15 s later the tail-end enters the tunnel
The train length will be how far the train travels in 15 s @ 120 k/hr
15 s = 15/3600 hr
rate * time = distance ( or length in this case)
15 / 3600 hr * 120 k/hr = .5 km or 500 meters long
