Question
Train A when travelling with a speed of 72 km/h crosses
a pole in 12 seconds. Find the time taken by the train A to cross another train B of length 40% more than that of train A which is coming from the opposite direction with a speed of 108 km/h.Solution
Speed of train A = 72 × 5/18 = 20 m/s
Length of train A = 20 × 12 = 240 metres
Length of train B = 1.4 × 240 = 336 metres
Speed of train B = 108 × 5/18 = 30 m/s
Relative speed = 20 + 30 = 50 m/s (opposite direction)
Total distance = 240 + 336 = 576 metres
Desired time = 576/50 = 11.52 seconds
(408 × 680)÷(20% of 680) = (250 × 260)÷ 10 + ? – 4500
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