Question
Two trains of equal lengths take 10 seconds and 15 seconds respectively to cross a telegraph post. If the length of each train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction?
Answer: Option B
$$\eqalign{
& {\text{Speed}}\,{\text{of}}\,{\text{the}}\,{\text{first}}\,{\text{train}} \cr
& = {\frac{{120}}{{10}}} \,{\text{m/sec}} \cr
& = 12\,{\text{m/sec}} \cr
& {\text{Speed}}\,{\text{of}}\,{\text{the}}\,{\text{second}}\,{\text{train}} \cr
& {\frac{{120}}{{15}}} \,{\text{m/sec}} \cr
& = 8\,{\text{m/sec}} \cr
& {\text{Relative}}\,{\text{speed}} = {12 + 8} = 20\,{\text{m/sec}} \cr
& \therefore {\text{Required}}\,{\text{time}} \cr
& = {\frac{{ {120 + 120} }}{{20}}} \,{\text{ sec}} \cr
& = 12\,{\text{sec}} \cr} $$
Was this answer helpful ?
$$\eqalign{
& {\text{Speed}}\,{\text{of}}\,{\text{the}}\,{\text{first}}\,{\text{train}} \cr
& = {\frac{{120}}{{10}}} \,{\text{m/sec}} \cr
& = 12\,{\text{m/sec}} \cr
& {\text{Speed}}\,{\text{of}}\,{\text{the}}\,{\text{second}}\,{\text{train}} \cr
& {\frac{{120}}{{15}}} \,{\text{m/sec}} \cr
& = 8\,{\text{m/sec}} \cr
& {\text{Relative}}\,{\text{speed}} = {12 + 8} = 20\,{\text{m/sec}} \cr
& \therefore {\text{Required}}\,{\text{time}} \cr
& = {\frac{{ {120 + 120} }}{{20}}} \,{\text{ sec}} \cr
& = 12\,{\text{sec}} \cr} $$
Was this answer helpful ?
More Questions on This Topic :
Latest Videos
Latest Test Papers
Submit Solution