A train 360 m long is running at a speed of 45 km/hr. In what time will it pass a bridge 140 m long?

Explanation:-

$$\eqalign{ & {\text{Formula}}\,{\text{for}}\,{\text{converting}}\,{\text{from}}\,{\text{km/hr}}\,{\text{to}}\,{\text{m/s:}} \cr & X\,{\text{km/hr}} = \left( {X \times \frac{5}{{18}}} \right)\,{\text{m/s}} \cr & {\text{Therefore,}}\,{\text{Speed}} \cr & = \left( {45 \times \frac{5}{{18}}} \right)\,{\text{m/sec}} = \frac{{25}}{2}{\text{m/sec}} \cr & {\text{Total}}\,{\text{distance}}\,{\text{to}}\,{\text{be}}\,{\text{covered}} \cr & = \left( {360 + 140} \right)m = 500\,m \cr & {\text{Formula}}\,{\text{for}}\,{\text{finding}}\,{\text{Time}} \cr & = \left( {\frac{{{\text{Distance}}}}{{{\text{Speed}}}}} \right) \cr & \therefore {\text{Required}}\,{\text{time}} \cr & = \left( {\frac{{500 \times 2}}{{25}}} \right)\,\sec \cr & = 40\,\sec . \cr}$$