A parrot flying above and parallel to a railway track crosses a moving train. The time of
crossing doubles if the parrot reverses its
direction of flight. If v is the velocity of the parrot,
then that of the train is
(b) 3 v
(c) 4 v
(e)
E/M/D
3
(a) 2 v
(d) 6 v

it has to be b, about 97 percent.

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me

the awnser is d you right bro