In a nuclear reaction , A decays to B emitting alpha particle. If B = 240 mass number(240 u) and alpha particle has a mass of 4u. By conservation of momentum , 0 = 240 v1 + 4 v2. The speed of alpha = 60 v1. The ke of alpha particle is
1/2 (4u) (60 v1)2 which is 60 times the KE of B. In terms of percentage KE of alpha is 98%(60/61) of the total KE .
The alpha particle has 98% of the kinetic energy. Nuclear reactions is also an application of conservation of momentum.