A train is running at a speed of 40 km/hr and it crosses a post in 18 seconds.…

When an object crosses a stationary point — such as a post, pole, or signal — the distance it travels in the given time is exactly equal to its own length. To convert a speed from km/hr to m/s, multiply by 5/18 (since 1 km = 1000 m and 1 hr = 3600 s, so 1 km/hr = 1000/3600 m/s = 5/18 m/s).

1. Convert the speed: 40 km/hr × 5/18 = 200/18 = 100/9 m/s.

2. Since the train crosses a stationary post, the distance covered equals the length of the train.

3. Apply Distance = Speed × Time: Length = 100/9 × 18 = 200 m.

Cross-check: 200 m covered in 18 s is a speed of 200/18 = 100/9 m/s; converting back to km/hr, 100/9 × 18/5 = 40 km/hr — matching the given speed, confirming the length is 200 m.