Question

(a)
120 मीटर और 80 मीटर लंबाई वाली दो ट्रेनें विपरीत दिशा में 42 किमी./घंटा' व
30 किमी./घंटा की रफ्तार से चल रही हैं। उन्हें एक दूसरे को पार करने में कितना समय लगेगा?
(पाठ-2 देखें)
Two trains 120m and 80m in length are travelling in opposite directions with velocities
42 kmh-' and 30 kmh-' respectively. How much time will they require to completely cross
each other?
(See Lesson 2)​

Answer 1

Given:

Two trains 120m and 80m in length are travelling in opposite directions with velocities

42 kmh-' and 30 kmh-' respectively.

To find:

Time taken to completely cross each other.

Calculation:

This question can be solved by the concept of relative velocity;

$\boxed{ \sf{time \: taken = \dfrac{total \: length \: of \: both \: trains}{relative \: velocity} }}$

$= > \sf{time \: taken = \dfrac{l1 + l2}{relative \: velocity} }$

Since the trains are moving in opposite directions,the relative velocity of one train with respect to another will be v1 + v2;

$= > \sf{time \: taken = \dfrac{l1 + l2}{v1 + v2} }$

$= > \sf{time \: taken = \dfrac{ \frac{(120 + 80)}{1000} }{(42 + 30)} }$

$= > \sf{time \: taken = \dfrac{ \frac{(200)}{1000} }{(42 + 30)} }$

$= > \sf{time \: taken = \dfrac{ 0.2 }{72} }$

$= > \sf{time \: taken = 0.0027 \: hr}$

$= > \sf{time \: taken = 10 \: sec}$

So, final answer is:

$\boxed{ \sf{time \: taken = 10 \: sec}}$