Question

TWO TRAINS 90m and 120mm in length are running opposite directions on parallel track with velocities 72km/h and 36km/h. find time at which they cross each other​

Answer 1

Given : ( Correction )

Two trains 90m and 120m in length are running opposite directions on parallel track with velocities 72 km/h and 36 km/h

To Find :

Time to completely cross

Formula Applied :

$\sf \bigstar\ \; \pink{Speed=\dfrac{Distance}{Time}}$

Solution :

Answer will be easy when you draw diagram for whole situation .

Distance = Length of train 1 + Length of train 2

               = 90 m + 120 m

               = 210 m

Relative speed = Speed of train 1 + Speed of train 2

                         =  72 km/h + 36 km/h

                         = 20 m/s + 10 m/s

                         = 30 m/s

$\sf Speed=\dfrac{Distance}{Time}\\\\\to \sf 30=\dfrac{210}{Time}\\\\\to \sf \green{Time=7\ s}\ \; \bigstar$

So , It takes 7 s to cross both trains each other

Answer 2

Answer:

$\tt {\pink{Given}}\begin{cases} \sf{\green{Length \: of \: 1^{st} \: train =90 \: m}}\\ \sf{\blue{Length \: of \: 2^{nd} \: train=120 \: m}}\\ \sf{\orange{Speed \: of \: 1^{st} \: train=72 \: km/hr}}\\ \sf{\red{Speed \: of \: 2^{nd} \: train=36 \: km/hr}}\end{cases}$

_____________________

$\dashrightarrow\:\: \sf Speed = \dfrac{Distance}{Time}$

$\dashrightarrow\:\: \sf 72 + 36 = \dfrac{120 + 90}{Time}$

$\dashrightarrow\:\: \sf 108 \times \dfrac{5}{18} = \dfrac{210}{Time}$

$\dashrightarrow\:\: \sf 30= \dfrac{210}{Time}$

$\dashrightarrow\:\: \sf Time = \dfrac{210}{30}$

$\dashrightarrow\:\: \underline{ \boxed{ \sf Time = 7 \: seconds}}$

$\therefore\underline{\textsf{ The time taken by two trains to cross each other is \textbf{7 seconds}}}.$