A) 7 s
B) \[7\frac{1}{2}\,\,\text{s}\]
C) 6 s
D) 10 s
Correct Answer: B
Solution :
If two trains be moving in opposite directions at rates u and v km/ h respectively, then their relative speed = (u + v) km/h Further if their lengths be x and y km. Then, time taken to cross each other \[=\frac{x+y}{u+v}h.\] Hence, total length \[=160+140=300\text{ m}\] Relative speed \[=(77+67)\] km/h = 144 km/h \[=144\times \frac{5}{18}=40m/s\] \[\therefore \] Time \[=\frac{300}{40}=7\frac{1}{2}s\]You need to login to perform this action.
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