# A 120m long train crosses a 280m long tunnel in 20 seconds. Find the time taken by train to cross a pole standing on a platform of length 500m.

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A 120m long train crosses a 280m long tunnel in 20 seconds. Find the time taken by train to cross a pole standing on a platform of length 500m.
1. 5 seconds
2. 7 seconds
3. 6.5 seconds
4. 6 seconds

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Correct Answer - Option 4 : 6 seconds

Given:

A 120m long train crosses a 280m long tunnel in 20 seconds.

Formula Used:

Time = [ L1 + L2] / Relative speed

Where, L1 = length of train; L2 = length of object that train is crossing

Relative Speed (RS) = Speed of train + speed of platform(= 0)

Calculation:

20 seconds = [120 + 280]/RS

⇒ 20 seconds = [120 + 280]/Speed of train [∵ speed of platform = 0]

⇒ Speed of train = 400/20 = 20 m/s

Now, time taken by train to cross the pole = Distance/Speed

Also, length of pole = 0 and speed of pole = 0

⇒ Time taken by train to cross the pole = Length of train / Speed of train

= 120/20 = 6 seconds