Question

A train travelling at 36 kmph crosses a platform in 20 seconds and a man standing on the platform in 10 seconds. What is the length of the platform in metres?

• A. 240 metres
• B. 100 metres
• C. 200 metres
• D. 300 metres

Hint:

Crossing a man gives the train's own length; crossing the platform gives train length plus platform length.

Answer 1

The Correct Option is B

A useful shortcut for this type of problem is to work directly with the extra distance covered because of the platform, instead of separately finding the train's length first.

1. Speed of the train in consistent units: $36 \times \frac{5}{18} = 10$ m/s.
2. In the 20 seconds it takes to cross the platform, compared to the 10 seconds it takes to cross a man, the train travels for an extra $20 - 10 = 10$ seconds.
3. This extra distance is exactly the length of the platform, since the man is a single point but the platform has length that the train must additionally cover.
4. Extra distance $= 10 \text{ m/s} \times 10 \text{ s} = 100$ m.

So the platform's length is 100 metres.

The correct answer is option B.