Take the 2-minute tour ×  A column of troops one km long is
moving along a straight road at a uniform pace. A messenger is
sent from the head of the column, delivers a message at the rear
of the column and returns. He also moves at a uniform pace and
arrives back at the head of the column when it has just covered
its own length. How far did the messenger travel?  I can't get
any ideas on how to start.  Thanks for any help.  share|improve
this question How far did the messenger travel means the
distance traveled or the displacement? If its displacement then
the answer should be 1km. –  Saurabh Jul 3 '12 at 6:10 It means
distance. –  Matt Jul 3 '12 at 6:12 You just need to organise
the information carefully and use distance = speed x time. Write
down what you know about the movement of the column - say speed
$u$ and the messenger say speed $v$ taking total time $t$. Split
the movement of the messenger into two obvious parts. Then
identify the total distance $d$ you want to find, and use the
information you have