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?

A. 20 sec
B. 45 sec
C. 50 sec
D. 40 sec

Solution:

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

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