An atom of uranium (m = 3.9529 10-25 kg) at rest decays spontaneously into an atom of helium (m= 6.6465 10-27 kg) and an atom of thorium (m = 3.8864 10-25 kg). The helium atom is observed to move in the positive x direction with a velocity of 1.423 107 m/s (Figure 1.2). (a) Find the velocity (magnitude and direc- tion) of the thorium atom. (b) Find the total kinetic energy of the two atoms after the decay. (a) (b) VTh Th y " | u U y He VHe X X