Multiple choice

A train is moving with an uniform speed. It crosses a railway platform 120 metres long in 12 seconds and another platform 170 metres long in 16 seconds. The speed of the train per second is ___________.

  1. $\displaystyle12\frac{1}{2}\:m/sec$

  2. 10 m/sec
  3. $\displaystyle10\frac{5}{10}\:m/sec$
  4. $\displaystyle10\frac{1}{2}\:m/sec$
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A Correct answer
Explanation

Let v be speed and L be train length. (L+120)/v = 12 and (L+170)/v = 16. L+120 = 12v and L+170 = 16v. Subtracting gives 50 = 4v, so v = 12.5 m/s.

AI explanation

Let the train's length be L and its speed be S. From the given information, L plus 120 equals 12S, and L plus 170 equals 16S. Subtracting the first equation from the second gives 50 equals 4S, so the speed S is 12.5 m/sec. This can also be written as 12 and 1/2 m/sec.

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