Question
A train travelling at the speed of 72 km/hr crosses
another train, having 20 meters less length and travelling in opposite direction at the speed of 54 km/hr in 8 seconds. If the longer train crosses a platform in 16 seconds, then the shorter train will cross the same platform in how many seconds?Solution
Speed of longer train = 72 × (5/18) = 20 m/s
Speed of shorter train = 54 × (5/18) = 15 m/s
Let length of longer and shorter trains be ‘L’ meters and (L – 20) metres, respectively.
According to question,
L + L – 20 = (20 + 15) × 8 = 280
2L – 20 = 280
L = 150 metres
So, L – 20 = 130 metres
Let length of platform is ‘P’ metres
So, P + 150 = 20 × 16 = 320
P = 320 – 150 = 170 meters
Desired time = (170 + 130)/15 = 300/15 = 20 seconds
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