A man walking towards the trains with a speed is 3 km/hr. How many seconds will a 500 metre long train cross a man if the speed of the train is 63 km/hr?

Speed of the train relative to man = (63 - 3) km/hr

                                                 = (60  * 5/18) m/sec

                                                 = 50/3 m/sec

Time to pass a man                     = 500/(50/3) sec

                                                 = (500 * 3) / 50

                                                 = 30 sec