A Uranium Nucleus (Mass 238 Units)at Rest Decays into a Helium

Multiple Choice

A uranium nucleus (mass 238 units) at rest decays into a helium nucleus (mass 4.0 units) and a thorium nucleus (mass 234 units) .If the speed of the helium nucleus is 5.5 × 10⁵ m/s,what is the speed of the thorium nucleus?

A) 9.4E+3 m/s
B) 3.2E+7 m/s
C) 3.4E+3 m/s
D) 9.4E+7 m/s
E) 1.9E-1 m/s