A toward B, B toward C, C toward D and D toward A, at a 1 km/s speed.

Of course, while A is flying, B also, hence A must change direction to keep aiming at B, this is also true for each of the 4 rockets...

When will the rockets meet ?

Solution

Same question with just 3 rockets at vertices of an equilateral triangle with sides 30 km.

Solution

Same question with 6 rockets at the verrtices of a regular hexagon with sides 30 km.

Solution