Question:

A train 300 meters long is running at a speed of 25 meters per second, it will cross a bridge 200 meters long in

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The train clears the bridge only when its last coach leaves it, so the distance is train length plus bridge length, that is 300 plus 200. Then divide by the speed.
Updated On: Jul 17, 2026
  • 5 seconds
  • 10 seconds
  • 20 seconds
  • 25 seconds
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The Correct Option is C

Solution and Explanation

Step 1: Work out what "cross the bridge" really means.
A train has length, so it is not a point. Crossing a bridge starts the moment the engine reaches the near end of the bridge and finishes only when the last coach clears the far end.
In that time the train's front travels the length of the bridge plus the full length of the train. This is the one idea the question tests, and missing it is the most common mistake.

Step 2: Add the two lengths to get the distance.
Total distance = length of train + length of bridge
\[ d = 300 + 200 = 500 \text{ metres} \]

Step 3: Use the speed-time relation.
The basic formula is
\[ \text{time} = \frac{\text{distance}}{\text{speed}} \]
The speed is already given in metres per second and the distance is in metres, so the units match and no conversion is needed.

Step 4: Put the numbers in.
\[ t = \frac{500}{25} = 20 \text{ seconds} \]

Step 5: Check the wrong options.
Option (A) 5 seconds is what you get if you wrongly divide only the bridge length by 25 after a slip, or divide 500 by 100. It is far too small.
Option (B) 10 seconds comes from using only the bridge length, \( \frac{200}{25} = 8 \), or from ignoring the train's own length in some rough way. Either way it forgets that the whole train must clear the bridge.
Option (D) 25 seconds simply copies the speed figure and has no working behind it.
Only 20 seconds uses the correct total distance of 500 metres.

Final Answer:
The train needs 20 seconds to cross the bridge completely.
\[ \boxed{20 \text{ seconds}} \]
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