Final answer:
The total momentum of two football players after colliding on the field, in the absence of external forces, remains the same, at 450 kg⋅m/s north.
Step-by-step explanation:
The total momentum before the collision was 450 kg⋅m/s to the north, and since momentum is conserved in collisions in the absence of external forces, their total momentum after the collision will also be 450 kg⋅m/s north. This conservation of momentum occurs because the forces each player experiences during the collision are equal in magnitude and opposite in direction, according to Newton's third law. This principle applies irrespective of whether the players bounce off each other or cling together after the collision, as long as no external forces are involved.