Question

Two trains move in opposite direction along parallel tracks. Both of them are 100 m long and each travelling with a velocity of 12.5 m/s. How long will it take for the first train to cross the second train?
8s
4s
6s
20s​

Answer 1

Answer:

Answer

Correct option is

B

4s

Total lenght to cross L=50+50=100m

relative velocity (w.r. t. other train)

v=15−(−10)=25m/s

∴t=

v

L

=

25

100

=4s

Answer 2

Solution :-

given that,

→ Length of first train = Length of second = 100 m

→ Velocity of first train = Velocity of second train = 12.5 m/s

so,

→ Relative distance = Length of first train + Length of second = 100 + 100 = 200 m

and,

→ Relative Velocity (In opposite direction) = Velocity of first train + Velocity of second train = 12.5 + 12.5 = 25 m/s .

then,

→ Time = Distance / Speed .

therefore,

→ Time taken by first train to cross the second train = Relative distance / Relative Velocity = 200 / 25 = 8 seconds (A) (Ans.)

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