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A train crosses a 500 m long platform in 2 minutes at the speed of 72 km/hr, then find in how much time it crosses another train of same length travelling at a speed of 108 km/hr in opposite direction.1. 76 seconds2. 84 seconds3. 96 seconds4. 120 seconds5. None of these |
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Answer» Correct Answer - Option 1 : 76 seconds Given: The speed of train = 72 km/hr The length of platform = 500 m The speed of another train = 108 km/hr Formula used: Distance = speed × time Concept used: To convert speed from km/hr to m/s the multiply with 5/18 Relative speed concept, Speed of both trains will add when the train moves in the opposite direction Speed of both the train will subtract when the train moves in the same direction Calculation: Let the length of train be l Now, Distance = speed × time ⇒ l + 500 = 72 × 5/18 × 120 ⇒ l = 1900 m The total length of both the train = 2 × 1900 = 3800 m Both trains moving in the opposite direction so speed = (20 + 30) = 50 m/s Time = 3800/50 = 76 second ∴ The time taken to cross another train is 76 seconds |
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