4. Two trains of equal lengths take 10 seconds and 15 sec-onds respect

1.	4. Two trains of equal lengths take 10 seconds and 15 sec-onds respectively to cross a telegraph post. If the lengthof each train be 120 metres, in what time (in seconds)tion?will they cross each other travelling in opposite direc-A. 12B. 14C. 16D. 20
Answer» Crossing the light post means crossing the length of the train. So, the speed of the 1st train is=120/10=12m/s The speed of the 2nd train is=120/15=8m/s Crossing each other means covering the total distance of two trains i.e (120+120)=240m And as the trains are moving in opposite direction their net speed will be =(12+8)m/s=20m/s. So, the time needed to crosses each other is=240÷20= 12 s.

4. Two trains of equal lengths take 10 seconds and 15 sec-onds respectively to cross a telegraph post. If the lengthof each train be 120 metres, in what time (in seconds)tion?will they cross each other travelling in opposite direc-A. 12B. 14C. 16D. 20

Answer»

Crossing the light post means crossing the length of the train.

So, the speed of the 1st train is=120/10=12m/s

The speed of the 2nd train is=120/15=8m/s

Crossing each other means covering the total distance of two trains i.e (120+120)=240m

And as the trains are moving in opposite direction their net speed will be =(12+8)m/s=20m/s.

So, the time needed to crosses each other is=240÷20= 12 s.