设质子质量m
动量守恒:(4m)v0=(4m)v1+mv2
动能守恒:0.5*(4m)v0^2=0.5*(4m)v1^2+0.5*m*v2^2
解得v1=0.6v0=600m/s,v2=1.6v0=1600m/s