A train 100 m long is running at the speed of 30 km/hr. The time (in second) in which it passes a man standing near the railway line is :

$$\eqalign{ & {\text{Speed : }} \cr & = {\text{ }}30{\text{ }}km/hr \cr & = {\text{ }}30 \times \frac{5}{{18}}{\text{ }}m/\sec \cr & = \frac{{25}}{3}m/\sec \cr & {\text{So, time = }}\frac{D}{S} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{100}}{{\frac{{25}}{3}}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 12 \,\,\text{seconds} \cr} $$