A 10. kg piece of thorium at rest suddenly decays into an 8.0 kg sample of radon that is traveling very quickly. What is the velocity of the 8.0 kg sample?
A 15 kg mass at rest decays into a 10 kg mass. How fast is the 10 kg mass moving?
A 20.0 kg mass at rests decays into a particle that is moving at 0.30c. What is the mass of this new particle?