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1. A train 108 m long moving at a speed of 50 km/hr crosses a train 112 m long coming from opposite direction in 6 seconds. The speed of the second train is:

A. 48 km/hr

B. 54 km/hr

C. 66 km/hr

D. 82 km/hr

Solution:

\begin{aligned} Let the speed of the second train be x km/hr . \\ Relative speed \\ = (x + 50) km/hr \\ = [(x + 50) \times \frac{5}{18}] m/sec \\ = \frac{250 + 5 x}{18} m/sec \\ Distance covered \\ = (108 + 112) = 220 m \\ ∴ \frac{220}{\frac{250 + 5 x}{18}} = 6 \\ \Rightarrow 250 + 5 x = 660 \\ \Rightarrow x = 82 km/hr \end{aligned}

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