How long will a train, 120 m long, take to clear a platform, 130 m long, if its speed is 50 km/hr?

Length of the train=120 m

Since the stationary object is not negligible.

Therefore, distance travelled= length of the train + length of the platform = 120+130 =250m

Since, the speed = 50 km/hr and distance= 250 m or 25/100 km

I.e. time= distance / speed = (25/100)/50 = 1/200 hrs or 18 seconds