Question

Two trains A and B of 150 m and 300 m, run at speed of 65 km/hr and 80 km/hr respectively, in the opposite direction to each
other. Find the time required to cross each other after the moment they met?​

Answer 1

Relative speed =(65+80)km/hr=(145×  5/18 )m/sec

Distance covered in crossing each other =(150+300)m=450m

Required time =  distance /speed=324/29sec

Answer 2

The trains are moving in the opposite directions, their relative speed is the sum of their individual speed.

⇒ relative speed of the trains= (65 km/ hr + 80 km /hr )

                                                =$145 km / hr$ ×5/18 m/sec = 145 ×5/18 m/ sec

Time taken by trains to cross each other = sum of the total length of the trains / their relative speed.

∴ sum of the total length of the trains =( 150m + 300m) = 450 m

Time taken by two trains to cross each other = $\frac{450}{145}$ ×$\frac{18}{5}$

                                                                          = 18 × 18 / 29  

                                                                           = $\frac{324}{29}$

                                                                            =$11.17 sec$

Ans :- After 11.17 sec the trains will cross each other,