Question

Nayjivan Express starts from Ahmedabad towards Baroda at 6:30 am in the morning, moving at an average speed of 50 km/h. The distance between Baroda and Ahmedabad is 100 km. At 7:00 am in the morning the Howrah Ahmedabad express starts from Baroda and moves towards Ahmedabad at 40 km/h. At 7:30 am, Mr. Shah, the station controller, realizes that both the trains are running on the same track. How much time does he have to take action to prevent the collision?

• A. 15 min
• B. 20 min
• C. 25 min
• D. 30 min

Hint:

Always calculate the relative speed when two objects are moving towards each other.

Answer 1

The Correct Option is B

At 7:30 am, the first train has already travelled 50 km/h × 1 hour = 50 km, and the second train has travelled 40 km/h × 0.5 hour = 20 km. Now, the relative speed between the two trains is 50 km/h + 40 km/h = 90 km/h. The remaining distance is 100 km − 50 km − 20 km = 30 km. Time required to cover 30 km at a relative speed of 90 km/h is \( \frac{30}{90} = \) 20 minutes.