Question
Two trains ‘T7’ and ‘U7’ of lengths 540 metres and
360 metres respectively are travelling towards each other. Ratio of speed of ‘T7’ to ‘U7’ is 3:1. If the trains take 45 seconds to cross each other from the time they meet, then find the average of speeds (in km/h) of trains ‘T7’ and ‘U7’.Solution
Let the speed of ‘T7’ and ‘U7’ be ‘3y’ and ‘1y’ m/s respectively.
Relative speed = 3y + 1y = 4y m/s
ATQ,
4y × 45 = 540 + 360
⇒ 180y = 900
⇒ y = 5
Therefore, required average = (3y + 1y) ÷ 2 = 2.0y
= 2.0 × 5 = 10.0 m/s = 10.0 × (18/5) = 36 km/h
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