Final answer:
The total momentum of both the blue and red cars before the explosion is 0 kg·m/s, and it remains 0 kg·m/s after the explosion due to the law of conservation of momentum.
Step-by-step explanation:
The total momentum of a system before and after an explosion (or collision) must remain the same according to the law of conservation of momentum, provided no external forces are acting on the system. In the scenario involving the blue and red cars that move apart after an explosion, assuming the blue car with a mass of 2.0 kg and the red car with a mass of 0.5 kg were initially at rest, the total momentum before the explosion would be 0 kg·m/s because both cars were not moving.
After the explosion, even though the individual momenta of the cars might have non-zero values, the total momentum remains at 0 kg·m/s because the momentum gained by one car will be equal in magnitude and opposite in direction to the momentum gained by the other car, keeping the total system momentum constant.