A train moves past a telegraph post and a bridge 342 m long in 10 seconds and…
2023
A train moves past a telegraph post and a bridge 342 m long in 10 seconds and 20 seconds respectively. What is the speed of the train?
- A.
95 km/hr
- B.
98 km/hr
- C.
99 km/hr
- D.
100 km/hr
Attempted by 8 students.
Show answer & explanation
Correct answer: D
Solution: Let v be the speed of the train in metres per second (m/s) and L be the length of the train in metres.
Passing the telegraph post takes 10 s, so L = v × 10.
Passing the 342 m bridge takes 20 s, so L + 342 = v × 20.
Subtract the first equation from the second: (L + 342) − L = 342 = 20v − 10v = 10v, so v = 342 / 10 = 34.2 m/s.
Convert to km/h: v = 34.2 × 3.6 = 123.12 km/hr (approximately).
Conclusion: The train's speed is about 123.12 km/hr. None of the provided options equal this value, so the given choices are incorrect.