Two trains, one 157 m long and the other 123 m long, are crossing each

1.	Two trains, one 157 m long and the other 123 m long, are crossing each other in opposite directions in 7.2 seconds. The combined speed of two trains every hour will be:1. 70 km/hr2. 105 km/hr3. 280 km/hr4. 140 km/hr
Answer» Correct Answer - Option 4 : 140 km/hr Given: Length of train 1 = 157 m Length of train 2 = 123 m Time taken to cross each other in opposite direction = 7.2 s Concept used: Time taken by trains to cross each other in the opposite direction, t = (L₁ + L₂)/(S₁ + S₂) Where S₁ and S₂ are speeds of trains 1 and 2 respectively. s m/s = s × (18/5) km/hr Calculation: 7.2 = (157 + 123)/(S₁ + S₂) ⇒ (S₁ + S₂) = 280/7.2 m/s ⇒ 280/7.2 × (18/5) = 140 km/hr ∴ The combined speed of both trains is 140 km/hr.

Two trains, one 157 m long and the other 123 m long, are crossing each other in opposite directions in 7.2 seconds. The combined speed of two trains every hour will be:1. 70 km/hr2. 105 km/hr3. 280 km/hr4. 140 km/hr

Answer» Correct Answer - Option 4 : 140 km/hr

Given:

Length of train 1 = 157 m

Length of train 2 = 123 m

Time taken to cross each other in opposite direction = 7.2 s

Concept used:

Time taken by trains to cross each other in the opposite direction, t = (L₁ + L₂)/(S₁ + S₂)

Where S₁ and S₂ are speeds of trains 1 and 2 respectively.

s m/s = s × (18/5) km/hr

Calculation:

7.2 = (157 + 123)/(S₁ + S₂)

⇒ (S₁ + S₂) = 280/7.2 m/s

⇒ 280/7.2 × (18/5) = 140 km/hr

∴ The combined speed of both trains is 140 km/hr.

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