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Two trains 121 m and 99 m in length are ...

Two trains 121 m and 99 m in length are running in opposite directions with velocities `40 km h^(-1)` and `32 km h^(-1)`. In what time they will completely cross each other?

A

9 s

B

11 s

C

13 s

D

15 s

Text Solution

Verified by Experts

The correct Answer is:
(b)
Here, `v_A = 40 km h^(-1), v_B = -32 km h^(-1)`
Length of train A, `l_A = 121` m, Length of train B, `l_b` = 99 m
Relative velocity of two trains is given by
`v_(AB) = v_A - v_B = 40 - (-32) = 72 km h^(-1) = 72 xx 5/18 = 20 m s^(-1)`
Total distance to be travelled by each train for completely crossing the other train `= 121 + 99 = 220` m
Time taken by each train to cross the other train `= 220 / 20 = 11` s
Hence the two trains will cross each other in 11 s.
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