Question
Two trains are running at 40 km/hr and 20 km/hr respectively in the same direction. Fast train completely passes a man sitting in the slower train in 5 seconds. What is the length of the fast train?
Answer: Option C
$$\eqalign{
& {\text{Relative}}\,{\text{speed}} = \left( {40 - 20} \right)\,{\text{km/hr}} \cr
& = \left( {20 \times \frac{5}{{18}}} \right)\,{\text{m/sec}} \cr
& = {\frac{{50}}{9}} \,{\text{m/sec}} \cr
& \therefore {\text{Length}}\,{\text{of}}\,{\text{faster}}\,{\text{train}} \cr
& = \left( {\frac{{50}}{9} \times 5} \right)\,m \cr
& = \frac{{250}}{9}\,m \cr
& = 27\frac{7}{9}\,m \cr} $$
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$$\eqalign{
& {\text{Relative}}\,{\text{speed}} = \left( {40 - 20} \right)\,{\text{km/hr}} \cr
& = \left( {20 \times \frac{5}{{18}}} \right)\,{\text{m/sec}} \cr
& = {\frac{{50}}{9}} \,{\text{m/sec}} \cr
& \therefore {\text{Length}}\,{\text{of}}\,{\text{faster}}\,{\text{train}} \cr
& = \left( {\frac{{50}}{9} \times 5} \right)\,m \cr
& = \frac{{250}}{9}\,m \cr
& = 27\frac{7}{9}\,m \cr} $$
Was this answer helpful ?
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