A 240-m long train passes a pole in 18 seconds and completely passes another…
2023
A 240-m long train passes a pole in 18 seconds and completely passes another train running in the opposite direction at a speed of 42 km/h in 17 seconds. What is the length of the other train?
- A.
170 m
- B.
185 m
- C.
195 m
- D.
200 m
Attempted by 23 students.
Show answer & explanation
Correct answer: B
Solution: Find the length of the other train.
Key idea: When two trains move in opposite directions, their relative speed is the sum of their speeds. The time taken to pass each other covers the sum of their lengths.
First train's speed = length / time = 240 m / 18 s = 13.33 m/s = 48 km/h.
Other train's speed is given as 42 km/h. Relative speed = 48 + 42 = 90 km/h = 25 m/s (since 1 km/h = 5/18 m/s).
Distance covered while crossing = relative speed × time = 25 m/s × 17 s = 425 m.
This distance equals sum of lengths: 240 m + other length = 425 m, so other length = 425 − 240 = 185 m.
Answer: The other train is 185 m long.