A train crosses a pole in 12 seconds and a 780-metre long tunnel in 72…
2024
A train crosses a pole in 12 seconds and a 780-metre long tunnel in 72 seconds. What is the length of the train?
- A.
156
- B.
172 m
- C.
186 m
- D.
136 m
Attempted by 17 students.
Show answer & explanation
Correct answer: A
Solution:
Let the length of the train be L metres. When the train crosses a pole it takes 12 s, so the speed of the train is L/12 m/s.
Time to cross the 780 m tunnel = (L + 780) / speed = (L + 780) / (L/12) = 12*(L + 780)/L.
Set this equal to the given tunnel-crossing time, 72 s: 12*(L + 780)/L = 72.
Solve: 12(L + 780) = 72L → L + 780 = 6L → 780 = 5L → L = 156.
Therefore, the length of the train is 156 m.