a 2.00kg cart travelling north at 4.00m/s collides head on with a 1.00kg cart travelling south at 8.00m/s. what is the magnitude of the total momentum of the two carts after the collision

Which of the following correctly describes what happens when an atomic bomb explodes? small pieces of fissionable material are joined and form a body with a mass greater than the critical mass, the relative number of neutrons escaping decreases, and a chain reaction and explosion result. large pieces of fissionable matter are brought together quickly and form a body with a mass smaller than the critical mass, the relative number of escaping neutrons increases, and a chain reaction and explosion result.