A 300 m long train running at 72 km/h passes a cyclist riding at 18 km/h in the same direction beside the track. How long does the train take to pass her?

Explanation

1. 01

   Same direction: relative speed = $72 - 18 = 54$ km/$h = 15$ m/s.

2. 02

   The train covers its own length relative to her: 300 m.

3. 03

   Time $= \frac{300}{15} = 20$ s.