Multiple choice

A $100\ m$ train is moving North at a speed of $16\ m s ^ { - 1 }$. A bird flying at 4 $m s ^ { - 1 }$ towards South crosses the train in

  1. $5 s$
  2. $10 s$
  3. $12 s$
  4. $20 s$
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A Correct answer
Explanation

Since the train and the bird are moving in opposite directions, their relative speed is the sum of their speeds: 16 + 4 = 20 m/s. The time taken to cross is distance / relative speed = 100 / 20 = 5 seconds.

AI explanation

Since the train and bird are moving in opposite directions, we add their speeds to find the relative speed: 16 m/s plus 4 m/s gives 20 m/s. The distance needed for the bird to cross the train is the length of the train, which is 100 m. Applying the time formula gives 100 m divided by 20 m/s, resulting in 5 s.

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