Question

12. A train 300 m long is travelling at a speed of
72 km/h and another train 250 m long is
travelling at a speed of 108 km/h. How
much time will they take to pass each other
completely if they are travelling in the opposite directions?
only answer if you know the answer please
please answer fast I have my math test which is going to start in 1 hour​

Answer 1

Given :

▪ Speed of train A = 72kmph

▪ Speed of train B = 108kmph

▪ Length of train A = 300m

▪ Length of train B = 250m

▪ They are travelling in the opposite direction.

To Find :

↗ Time taken by them to pass each other.

Explanation :

✴ Speed of train A wrt train B :

$\leadsto\sf\:V_{AB}=V_A-V_B$

$\leadsto\sf\:V_{AB}=72-(-108)$

[Negative sign of speed of train B shows opposite direction.]

$\leadsto\sf\:V_{AB}=180\:kmh^{-1}$

⇒ 1kmph = 5/18mps

⇒ 180kmph = 180×5/18 = 50mps

✴ Time taken by them to pass each other :

➝ Total distance covered by each train = 300 + 250 = 550m

$\mapsto\sf\:speed=\dfrac{distance}{time}$

$\mapsto\sf\:50=\dfrac{550}{Time}$

$\mapsto\boxed{\bf{Time=11\:s}}$

Answer 2

$\large\bf{\underbrace{\purple{SOLUTION:-}}}$

GIVEN :-

☞ Let two trains be the Train ‘A’ and Train ‘B’ .

▼ Length of Train ‘A’ = 300 m

▼ Length of Train ‘B’ = 250 m

▼ Speed of Train ‘A’ = 72 km/h

▼ Speed of Train ‘B’ = 108 km/h

CONVERSION :-

• 1 km/h = 1000/3600 m/s = 5/18 m/s

▼ So,

☞ Speed of Train ‘A’ = 72 km/h = 20 m/s

☞ Speed of Train ‘B’ = 108 km/h = 30 m/s

To Find :-

• Time that they will take to pass each other completely, if they are travelling in the opposite direction .

CALCULATION :-

☞ First of all find the relative velocity between them.

$\large\rm{V_{AB}\:=\:V_A\:-\:V_B\:}$

$\large\rm{\implies\:V_{AB}\:=\:20\:-\:(-30)\:}$

✪ [Speed of Train ‘B’ is in the opposite direction, so it was taken as (-ve).]

$\large\rm{\boxed{\implies\:V_{AB}\:=\:50\:m/s\:}}$

☞ Now, find the total distance travelled by each train .

$\large\rm{Total\:distance\:=\:300\:m\:+\:250\:m\:}$

$\large\rm{\boxed{\implies\:Total\:distance\:=\:550\:m\:}}$

☞ Now, put the below formula and get the Answer .

FORMULA :-

$\checkmark\:\sf\underline{\green{\boxed{Time\:=\:\dfrac{Total\:Distance}{(Velocity)_{rel}}\:}}}$

__________________________

$\rm{\implies\:Time\:=\:\dfrac{550}{50}\:}$

$\rm{\red{\boxed{\implies\:Time\:=\:11\:sec\:}}}$