Basic question about time dilation

if 2 space ships are moving with respect to an observer with same speed
one spaceship shoots a light beam to the other and it reflects it back. this path of light is V shaped for the observer, why?
shouldn't it be a straight line and miss the second spaceship.

http://upload.wikimedia.org/wikipedia/co…

Forget the relativity.

Imagine you and your friend are driving separate cars in the same direction. You toss a ball to your friend, who immediately throws it back. What path does the ball take? A v-shape.

(Ignore air resistance.)