The law of what energy states that energy cannot be created or destroyed

What is the momentum of a 2 kg object moving at 15 meters per second

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.

While the change in blank will remain the same during a collision, the force needed to bring an object to a stop can be blank if the time if collision is blank