A uranium-238 nucleus,initially at rest,emits an alpha particle with a speed of 1.4×107 m/s.Calculate the recoil speed of the residual nucleus thorium-234.Assume that the mass of a nucleus is proportional to the mass number.+
When a U238 nucleus originally at rest decays by emitting an alpha particle having a speed ‘u’, the recoil speed of the residual nucleus is