Question

Two trains 126 m and 114 m long are running in opposite directions, one at the rate of 30kmph and another one at 42kmph. From the moment they meet will cross each other in

Answer 1

Relative speed of the trains=72kmph=20m/s
Total distance to be traveled=240m
so time required=12 seconds

Answer 2

Answer:

In 12 seconds both trains will cross each other

Step-by-step explanation:

Length of first train = 126 meters

Speed of first train = 30 km/hour

Length of second train = 114 meters

Speed of second train = 42 km/hour

Now, the train will cross each other when the starting point of one train will become the end point of other. So, the distance will be sum of their lengths ⇒ Distance = 126 + 114 = 240 meters

As they are travelling in the opposite direction so the speed of first will be added to the speed of the second ⇒ speed = 30 + 42 = 72 km per hour

Length of first train = 126 meters

Speed of first train = 30 km/hour

$\text{Total speed of trains in meters per second =}\frac{72\times 1000}{3600}$

$\text{Time taken to cross each other = }\frac{Distance}{Speed}\\\\\implies Time=\frac{240}{\frac{72\times 1000}{3600}}=\frac{240}{72\times 1000}\times 3600\\\\\bf\implies Time=12\textbf{ seconds}$

Hence, In 12 seconds both trains will cross each other