Question

Two trains 120 m and 80 m n length are running in opposite directions with velocities 42kmph and 30 kmph. In what time they will completely cross each other?
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Answer 1

Given :-

Length of the two trains = 120 m and 80 m

Velocity of the two trains travelling = 42 km/h and 30 km/h

To Find :-

The time when they will completely cross each other.

Analysis :-

Firstly, add up the total distance and the total speed of the trains.

Then substitute the values we got such that time is equal to total distance by total speed and find the time they'll completely cross each other accordingly.

Solution :-

We know that,

• s = Speed
• d = Distance
• t = Time

Total distance,

Given that,

Distance₁ = 120 m

Distance₂ = 80 m

Substituting their values,

Total distance = d₁ + d₂

⇒ 120 + 80

⇒ 200 m

Total speed,

Given that,

Speed₁ = 42 km/h

Speed₂ = 30 km/h

Substituting their values,

Total speed = s₁ + s₂

⇒ 42 + 30

⇒ 72 km/h

Using the formula,

$\underline{\boxed{\sf Time=\dfrac{Total \ distance}{Total \ speed} }}$

Given that,

Distance (d) = 200 m

Speed (s) = 72 km/h = 20 m/s

Substituting their values,

⇒ t = d/s

⇒ t = 200/20

⇒ t = 10 sec

Therefore, the time taken to complete crossing each other is 10 sec.

Answer 2

Answer:

Given :-

• Length of the two trains = 120 m and 80 m
• Velocity of the two trains travelling = 42 km/h and 30 km/h

To Find :-

Time they will completely cross each other?

Solution :-

So, we will first find total distance and speed of both

$\sf \: total \: distance = train1 + train2$

$\sf \: total \: distance = 120 + 80 = 200 \: m$

Now,

Let's find total speed

$\sf \: total \: speed \: = train1 + train2$

$\sf total \: speed = 30 + 42 \: = 72 kmph$

Now,

Let's convert the kmph into mps

Speed (s) = 72 km/h × 5/18 = 20 m/s

$\huge \bf \: Time = \frac{Distance}{Speed}$

$\sf \: Time = \dfrac{200}{20}$

$\sf \: Time \: taken = 10 \: sec$

Hence,

They will meet after 10 sec.