Two trains are moving in the same direction at 100 km/hr and 60 km/hr, respectively. The faster train crosses a man in the slower train in 9 seconds. What is the length of the faster train?
100 m
When two bodies move in the same direction, the relative speed is the difference of their speeds. To cross a man sitting in the slower train, the faster train covers only its own length at this relative speed.
Relative speed = 100 – 60 = 40 km/hr = \(40 \times \frac{5}{18} = \frac{100}{9}\) m/s.
Length of the faster train = relative speed × time = \(\frac{100}{9} \times 9 = 100\) m.
Check: a 100 m train moving at \(\frac{100}{9}\) m/s relative to the man passes him in \(100 \div \frac{100}{9} = 9\) seconds, as given.
Hence, 100 m.
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