Two trains 120 m and 80 m in length are running in opposite directions with velocities 42km/h and 30 km/h. In what time they will completely cross each other?
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Given :
- Length of train A = 120 m
- Length of train B = 80 m
- Velocity of train A = 42 km / hr
- Velocity of train B = 30 km / hr [ consider this train is moving in opposite direction ]
To find :
- Time in which the trains will completely cross each other
How to solve :
- Find the relative velocity of the train A wrt B
- Find total distance
- Substitute the value of distance and velocity in the formula in order to get time
Solution :
Total distance covered
= Length of train A + Length of train B
= 120 + 80
= 200 m
Total distance covered = 200m
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Relative velocity of train A wrt B
= 42 - (-30)
= 42 + 30
= 72 km / hr
In order to convert into km / hr into m/s multiply by 5 / 18
= 72 x 5 / 18
= 20 m /s
Relative velocity of train A wrt B = 20m/s .
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we know that ,
⇒ time = distance / velocity
⇒ time = 200 / 20
⇒ time = 10 s
The time taken by the trains to completely cross each other is 10 s .
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