​ How long does it take for a 200 m long train, moving at a speed of 72 km/h, to completely cross another 300 m long train moving at a speed of 36 km/h in the same direction?​

Correct option is D

Given:

- Length of first train = 200 m
- Speed of first train = 72 km/h = 72 × 5/18 = 20 m/s
- Length of second train = 300 m
- Speed of second train = 36 km/h = 36 × 5/18 = 10 m/s
 Formula Used:

Time = Total Distance / Relative Speed
 Solution:

Since both trains are moving in the same direction,
Relative Speed = 20 m/s - 10 m/s = 10 m/s
Total Distance to be covered = 200 m + 300 m = 500 m
Time = 500 / 10 = 50 seconds