Question

1. Two trains each of length 150 m are mov
opposite direction at 36 km/hr and 72
respectively. Time taken by them to just
each other completely is
(1) 4 s
(2) 6 s
(3) 8 s
(4) 10 s​

Answer 1

$\LARGE{ \underline{\underline{ \sf{Required \: answer:}}}}$

GiveN:

• Two trains of equal lengths are crossing each other in opposite direction.

• Their speeds are 36 km/hr and 72 km/hr

To FinD:

• Time taken to cross each other?

Step-by-Step Explanation:

When two train passes a moving object (having some length) in the opposite direction, they have to cover the sum of their lengths.

Hence,

⇒ Distance to be covered = 150 m × 2

⇒ Distance to be covered = 300 m

Their speeds are opposite to each other. Hence, the relative speed will be their sum.

Unit conversion first:

• 36 km/hr = 36 × 5/18 m/s = 10 m/s
• 72 km/hr = 72 × 5/18 m/s = 20 m/s

Relative speed:

= 10 m/s - (-20 m/s)

= 10 m/s + 20 m/s (Their sum)

= 30 m/s

Then,

Time taken by the two trains to cross each other = Sum of length of trains / Relative speed of trains

⇒ Time taken = 300 m / 30 m/s

⇒ Time taken = 10 s

Therefore,

The two trains crossed each other in 10 seconds.

$\huge{ \boxed{ \sf{ \red{Option \: D}}}}$

Answer 2

${\huge{\underline{\bf{\pink{♡Solution}}}}}$

☃️GiveN:-

✧Two trains of equal lengths are crossing each other in opposite direction.

✧Their speeds are 36 km/hr and 72 km/hr

☃️To FinD:

Time taken to cross each other?

☃️Step-by-Step Explanation:

When two train passes a moving object (having some length) in the opposite direction, they have to cover the sum of their lengths.

Hence,

⇒ Distance to be covered = 150 m × 2

⇒ Distance to be covered = 300 m

Their speeds are opposite to each other. Hence, the relative speed will be their sum.

Unit conversion first:

36 km/hr = 36 × 5/18 m/s = 10 m/s

72 km/hr = 72 × 5/18 m/s = 20 m/s

Relative speed:

= 10 m/s - (-20 m/s)

= 10 m/s + 20 m/s (Their sum)

= 30 m/s

Then,

Time taken by the two trains to cross each other = Sum of length of trains / Relative speed of trains

⇒ Time taken = 300 m / 30 m/s

⇒ Time taken = 10 s

Therefore,

The two trains crossed each other in 10 seconds.

Hence,the answer is

$\huge\mathfrak\red{Option \: D}$