Question

A uranium-238 atom can break up into a thorium-234 atom and a particle called an alpha particle, α-4. The numbers indicate the inertias of the atoms and the alpha particle in atomic mass units (1 amu = 1.66 × 10−27 kg). When an uranium atom initially at rest breaks up, the thorium atom is observed to recoil with an x component of velocity of -2.9 × 105 m/s. How much of the uranium atom's internal energy is released in the breakup?

Answer 1

"The numbers indicate the inertias of the atoms ... "

Which numbers?