Two trains, each 180 m long, are moving towards each other on parallel tracks at speeds of 50 km/hr and 70 km/hr. In how many seconds will they completely cross each other?

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  1. 10.4
  2. 10.2
  3. 10.8
  4. 10.6

Answer (Detailed Solution Below)

Option 3 : 10.8
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Detailed Solution

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Given:

Length of each train = 180 m

Speed of first train = 50 km/hr

Speed of second train = 70 km/hr

Formula used:

Relative speed when two objects move towards each other = Speed of first object + Speed of second object

Time taken to cross each other = Total distance / Relative speed

Calculation:

Relative speed = 50 km/hr + 70 km/hr

⇒ Relative speed = 120 km/hr

Convert speed to m/s:

⇒ 120 km/hr = 120 × (1000/3600) m/s

⇒ 120 km/hr = 33.33 m/s

Total distance = Length of first train + Length of second train

⇒ Total distance = 180 m + 180 m

⇒ Total distance = 360 m

Time taken to cross each other = Total distance / Relative speed

⇒ Time taken = 360 m / 33.33 m/s

⇒ Time taken = 10.8 seconds

∴ The correct answer is option (3).

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