Two trains 1000 m long are moving parallel to each other at a speed of 100 m/s and 150 m/s respectively. After what time they pass each other?

Options

A. 4s
B. 20 s
C. 8 s
D. 40 s

Answer

C

Explanation

With respect to the first train, the second train is approaching with a velocity of `(100 m/s + 150 m/s) = 250 m/s`. To completely cross the first train the second train has to travel a distance of 2000 m relative to first train.

`therefore` Time = `("Distance")/("Velocity") = (2000m)/(250 m//s) = 8 `sec
`D = 1000 + 1000 = 2000m`
`v = 150 + 100 = 250 m//s`
`2000 = 250 xx t`
`implies t = 8`