A 140 metre long train crosses another 210 metre long train running in

1.	A 140 metre long train crosses another 210 metre long train running in the opposite direction in 7 seconds. If the speed of the first train is 70 km/hr, what is the speed of the second train in km/h?1). 1002). 1103). 1404). Cannot be determined
Answer» Let the SPEED of the 210 m LONG train = x km/h As the trains are travelling in opposite directions, Relative speed of the first train w.r.t the second train = Speed of train 1 + Speed of train 2 ⇒ Relative speed = (70 + x)km/h = (70 + x) × 5/18 m/s---(1) Thus, Distance covered by train 1 = Length of Train 1 + Length of train 2 ⇒ Distance covered by train 1 = 140 + 210 = 350 m Time TAKEN = 7 seconds ∴ Relative speed × (Time taken) = Total distance covered ⇒ (70 + x) × (5/18) × 7 = 350 ⇒ (70 + x) × (5/18) = 50 ⇒ (70 + x)/18 = 10 ⇒ x = 110 km/h Thus, The speed of the second train is 110 km/h

A 140 metre long train crosses another 210 metre long train running in the opposite direction in 7 seconds. If the speed of the first train is 70 km/hr, what is the speed of the second train in km/h?1). 1002). 1103). 1404). Cannot be determined

Answer»

Let the SPEED of the 210 m LONG train = x km/h

As the trains are travelling in opposite directions,

Relative speed of the first train w.r.t the second train = Speed of train 1 + Speed of train 2

⇒ Relative speed = (70 + x)km/h = (70 + x) × 5/18 m/s---(1)

Thus,

Distance covered by train 1 = Length of Train 1 + Length of train 2

⇒ Distance covered by train 1 = 140 + 210 = 350 m

Time TAKEN = 7 seconds

∴ Relative speed × (Time taken) = Total distance covered

⇒ (70 + x) × (5/18) × 7 = 350

⇒ (70 + x) × (5/18) = 50

⇒ (70 + x)/18 = 10

⇒ x = 110 km/h

Thus,

The speed of the second train is 110 km/h

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