1.
速度变换ux1=0.9c,ux2=-0.9c,以飞船1为∑'系,则v=ux1=0.9c
ux2'=(ux2-v)/(1-v*ux/c^2)
=(-0.9c-0.9c)/(1+0.9*0.9)=(-1.8/1.81)c=-0.994475c
2.子弹1,u1x=V,u1y=0,子弹2,ux2=0,uy2=V,以子弹1为∑'系,则v=ux1=V,
子弹2相对于子弹1的速度为
ux2'=(ux2-V)/(1-V*ux2/c^2)=ux2-V=-V
uy2'=uy2*(1-(V/c)^2)^(1/2)/(1-V*ux2/c^2)=V*(1-(V/c)^2)^(1/2)