Two trains running towards each other on parallel tracks, at speeds of 45 km/hr and 51 km/hr, take 21 seconds to cross each other. If the length of one train is 290 m, then the length (in m) of the other train is:
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e 270.
Speed in m/s = Speed in km/hr × 5/18
Train A: 45 × 5/18 = 12.5 m/s
Train B: 51 × 5/18 = 14.17 m/s
Relative speed = 12.5 + 14.17 = 26.67 m/s
Time = Sum of lengths/Relative speed ⇒ 21 = (290 + x)/26.67
⇒ 290 + x = 21 × 26.67 = 560.07
⇒ x = 560.07 − 290 = 270.07 ≈ 270 m