[填空题]
An atomic nucleus initia260n(t xv2ly lnvjmf3lly moving at 420m/s emits an alpha particle in the dir4sgduph 3p7 p h:or/zf 97q*ojection of its velocity, and the remaininogpd/h3 jh 7z:p*9squ7p 4frog nucleus slows to 350m/s If the alpha particle has a mass of 4.0 u and the original nucleus has a mass of 222 u, what speed does the alpha particle have when it is emitted? m/s
