1.

A train of length 150 m takes 10 sec to pass over another train 100 m long coming from opposite direction. If the speed of the first train be 30 km/hr, the speed of the second train is (a) 54 km/hr (b) 60 km/hr (c) 72 km/hr (d) 36 km/hr

Answer»

(b) 60 km/hr

Let the speed of the second train = x km/hr 

Since both the trains are running in opposite directions. Their relative speed = (30 + \(x\)) km/hr = (30 + \(x\)) x \(\frac{5}{18}\) m/sec

∴ Time taken to pass another train = \(\frac{\text{Sum of the lengths of both the trains in metres}}{\text{Relative speed in m/sec}}\)

⇒ 10 = \(\frac{(150+100)}{(30+x)\times\frac{5}{18}}\)

⇒ (30 + \(x\)) = \(\frac{250\times18}{10\times5}\) = 90

⇒ \(x\) = (90 – 30) km/hr = 60 km/hr.


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