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A train of length 110 m is moving with a speed of 72 km/h and another train of length 120 m is moving with a speed of 36 km/h in opposite direction along parallel tracks. What is the time taken in seconds to cross each other?
1. \(\dfrac{23}{3}\) sec
2. 11.2 sec
3. 23 sec
4. 24 sec

1 Answer

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Best answer
Correct Answer - Option 1 : \(\dfrac{23}{3}\) sec

Given-

Length of 1st train = 110 m

Speed of 1st train = 72km/hr 

Length of 1st train = 120 m

Speed of 1st train = 36 km/hr 

Formula used = 

Distance = Speed × Time

Relative Speed = Speed of Object 1 + Speed of Object 2 ( If they are moving opposite to each other)

Concept Used- 

For a train to cross another train completely it should travel a distance equal to sum of length of both the trains.

Calculation-

Total distance to be covered = 110 + 120

= 230 m

Speed of 1st train = 72 × 5/18

= 20 m/sec

Speed of 1st train = 36 × 5/18

= 10 m/sec

Their relative Speed = 20 + 10

= 30 m/sec

Time taken to cross each other = 230/30

= 23/3 seconds

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