CareerCup

D: distance between 2 trains
v1,v2: speeds of two trains
v3: speed of bird(v3>v1 &&v3>v2)

1)Find the time taken to collide
T1=D/(v1+v2)

2)total distance traveled by the bird
D2=T1*v3

3)# of times bird makes a U turn
Maybe infinite (not sure)

hey i also think so

trains traveling in opposite directions never collide

trains traveling in opposite directions never collide

Train travelling in opposite direction may collide, train travelling in same direction may collide.. only one train can also collide with itself.. ask Indian Railway..
what about the poor bird.. its not even afraid of train whistle..it should die before the last three U turns. :)

u all are bastards

zglgjg is right.
No. of u turns is indefinite,the problem can be identified when there is too short a distance between the trains ie when they are about to collide.

what is the answer for the second part i.e number of trips made by bird? there will be a infinite series right ..but what is it?

Everybody know how to find the distance traveled by the bird. The attraction of the question is the second part... The answer will surprise you..... It depends on the size of the bird (If its a point then infinite, if it is not a point then why are we even solving such a puzzle :). BTW for the trains never colliding read: en.wikipedia.org/wiki/Zeno%27s_paradoxes

distance traveled: D/vb, where D is the initial distance and vb is the speed of the bird;

Time U turned: infinite. Suppose finite, at the last U turn, suppose the trains are d apart, in d/(vt + vb) time, the bird run into the other train, however the trains are still d(1 - 2vt/(vt + vb))>0 apart, which means there is another U turn. contradiction