Question
Two trains running on parallel track with lengths 140 m
and 40 m respectively. When travelling in opposite directions they are observed to pass each other in 10 seconds, but when they are running in the same direction at the rates as before, the faster train passes the other in 20 seconds. Find the speed of the two trains in km per hour.Solution
Let R1 = Relative speed, when moving in same direction = (140 + 40)/20 = 9 m/s R2 = Relative speed, when moving in opposite direction = (140 + 40)/10 = 18 m/s Now, Speed of faster train = (R1+R2)/2 = (9 + 18)/2 = 13.5 m/sec = 13.5 x 18/5 = 48.6 km/hr Speed of slower train = (R2-R1)/2 = (18-9)/2 = 4.5 m/s = 4.5 x 18/5 = 16.2 km/hr
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